LIBRARY 

UNIVERSITY  OF 
CALIFORNIA 


EARTH 

SCIENCES 
LIBRARY 


THE  LIBRARY 

OF 

THE  UNIVERSITY 
OF  CALIFORNIA 

PRESENTED  BY 

PROF.  CHARLES  A.  KOFOID  AND 
MRS.  PRUDENCE  W.  KOFOID 


REVISED 


TEXT-BOOK  OF  GEOLOGY 


BY 

JAMES   D.    DANA,   LL.D. 

LATE  PROFESSOR  OF  GEOLOGY  AND  MINERALOGY  IN  YALE  UNIVERSITY, 

AUTHOR  OF  "GEOLOGICAL  STORY  BRIEFLY  TOLD,"  "MANUAL  OF  GEOLOGY,' 

"SYSTEM  OF  MINERALOGY,"  "CHARACTERISTICS  OF  VOLCANOES," 

"CORALS  AND  CORAL  ISLANDS,"   EEPORTS  OF  WILKES' 

EXPLORING  EXPEDITION,  ON  GEOLOGY,  ZOO'PHYTES, 

AND  CRUSTACEA,  ETC. 


FIFTH  EDITION,   REVISED  AND  ENLARGED 


EDITED  BY 

WILLIAM  NORTH  RICE,  PH.D.,  LL.D. 

PROFESSOR  OF  GEOLOGY  IN  WESLEYAN  UNIVEESITT 


NEW  YORK  •:•  CINCINNATI  •:•  CHICAGO 

AMERICAN    BOOK    COMPANY 


JU. 


COPYRIGHT,  1897,  BY 
AMEKICAN  BOOK  COMPANY 


REV.    T.    B.    GEOL. 
W.    P.    8 


EARTH 

SCIENCES 
LIBRARY 


PREFACE. 


THE  late  Professor  Dana  had  begun  a  revision  of  this 
work  a  short  time  before  his  death.  The  request  of  his 
family  that  I  should  complete  the  work  of  my  revered 
teacher,  was  responded  to  with  something  like  a  feeling 
of  filial  obligation. 

It  was  proposed  in  the  plan  of  revision  that  the  distinc- 
tive characteristics  of  the  book  should  be  preserved  so  far 
as  possible.  It  was  to  be  brought  down  to  the  present 
time  as  regards  its  facts,  but  it  was  still  to  express  the 
well-known  opinions  of  its  author.  The  general  plan  of 
arrangement  was  to  be  kept  unchanged,  and  the  size  of 
the  book  to  be  increased  as  little  as  possible. 

In  the  progress  of  the  work  it  became  manifest  that  the 
usefulness  of  the  book  would  be  increased  by  certain 
changes  more  radical  than  had  been  at  first  contemplated. 
The  zoological  and  botanical  classifications  used  in  the 
former  edition  were  judged  to  be  obsolete.  The  endeavor 
has  been  made  to  substitute  for  them,  as  nearly  as  practi- 
cable, the  classifications  which  are  followed  in  the  major- 
ity of  recent  manuals  on  zoology  and  botany,  whether 
precisely  accordant  with  my  own  views  or  not.  It  was 
decided  that  the  theory  of  evolution  required  fuller  recog- 

iii 


iy  PEEFACB. 

nition  than  it  had  received  in  the  previous  edition  of  this 
work  or  the  last  edition  of  the  Manual.  It  was  a  proof 
of  Professor  Dana's  remarkable  hospitality  to  new  ideas, 
that  he  adopted  a  belief  in  evolution  at  an  age  when  most 
men  are  incapable  of  important  changes  of  opinion.  But 
the  idea  of  evolution  never  influenced  his  thinking  in 
general  as  it  doubtless  would  have  done  had  he  embraced 
it  earlier.  In  the  present  edition,  the  bearing  of  various 
events  in  geological  history  upon  the  theory  of  evolution 
is  pointed  out  in  the  appropriate  places;  and,  in  the 
closing  chapter,  which  has  been  entirely  rewritten,  the 
general  bearing  of  paleontology  upon  evolution  is  dis- 
cussed. The  treatment  of  metamorphism  also  was  be- 
lieved to  require  considerable  modification,  especially 
with  reference  to  dynamic  metamorphism  and  the  de- 
velopment of  a  foliated  structure  in  igneous  rocks. 

With  these  exceptions,  the  book  presents  substantially 
the  views  of  the  science  which  were  held  by  the  author  in 
his  later  years,  and  which  are  embodied  in  that  monumen- 
tal work,  the  fourth  edition  of  the  Manual.  I  have  been 
the  more  willing  to  follow  this  course,  since  in  the  main 
my  own  opinions  are  in  harmony  with  those  of  my  teacher ; 
although  on  a  few  points,  if  the  responsibility  for  the 
book  had  been  solely  my  own,  the  views  expressed  would 
have  been  somewhat  different,  as,  for  instance,  in  regard 
to  the  geographic  and  climatic  oscillations  of  the  Quater- 
nary era.  It  is  a  delicate  task,  in  revising  the  work  of 
another,  to  discriminate  between  errors  which  should  be 
corrected,  and  statements  at  variance  with  the  editor's 
opinions,  which,  in  deference  to  the  author,  should  be  left 


PREFACE.  V 

unchanged.  I  cannot  flatter  myself  that  questions  of  this 
sort  have  always  been  decided  aright.  I  have  doubtless 
sometimes  changed  too  much,  and  sometimes  too  little. 

The  only  important  change  in  the  arrangement  of  the 
book,  the  insertion  of  the  chapter  on  Zoological  and  Botan- 
ical Classification  before  the  chapter  on  Dynamical  Geol- 
ogy, was  indicated  in  the  notes  left  by  the  author.  The 
practice  followed  by  Professor  Dana,  in  previous  editions 
of  this  book,  and  in  his  other  works,  of  writing  the  names 
of  zoological  and  botanical  groups  with  anglicized  termi- 
nations, has  been  followed,  in  general,  in  this  edition. 
The  full  Latin  form  of  names  of  groups  above  the  grade 
of  family  has  been  used  only  in  cases  where  no  anglicized 
form  is  sanctioned  by  general  usage.  Professor  Dana's 
plan  of  terminating  names  of  rocks  in  yte,  in  distinction 
from  the  names  of  minerals  which  terminate  in  ite,  it  has 
been  deemed  best  to  abandon,  as  that  innovation  in  nomen- 
clature has  not  been  adopted  by  other  writers. 

The  appendix  to  the  former  edition,  giving  localities  of 
fossils,  has  been  omitted.  It  is  believed  that  such  a  list 
is  not  of  much  value  unless  given  in  more  detail  than  the 
space  at  disposal  would  permit.  Teachers  who  desire 
such  a  list  are  referred  to  Schuchert's  Directions  for  Col- 
lecting and  Preparing  Fossils,  published  as  Part  K  of  Bul- 
letin No.  39  of  the  United  States  National  Museum. 

I  take  this  opportunity  for  grateful  acknowledgments 
to  Professor  E.  S.  Dana,  Ph.D.,  for  his  appreciative  sym- 
pathy in  the  perplexities  of  my  work  ;  to  the  publishers, 
for  their  earnest  cooperation  in  the  endeavor  to  make  the 
book  as  good  as  possible  ;  to  G.  K.  Gilbert,  A.M.,  of  the 


VI  PREFACE. 

United  States  Geological  Survey,  for  valuable  criticisms 
on  the  manuscript ;  and  to  my  son,  Professor  E.  L.  Rice, 
Ph.D.,  for  assistance  in  the  correction  of  the  proof.  It  is 
hoped  that  the  book  in  its  revised  form  will  prove  itself 
adapted  to  the  use  of  students  in  our  schools  and  colleges, 
and  that  it  will  keep  before  their  minds  the  name  and  the 
scientific  work  of  one  of  the  greatest  of  geologists  and  one 
of  the  noblest  of  men. 

WILLIAM  NORTH  RICE. 


CONTENTS. 


PAGE 

INTRODUCTION.     AIM,  SUBJECTS,  AND  DIVISIONS  OF  GEOLOGY  .        1 

PART  I.     PHYSIOGRAPHIC  GEOLOGY. 

I.    GENERAL  FEATURES  OF  THE  EARTH'S  SURFACE         ...        7 
II.    SYSTEM  IN  THE  EARTH'S  FEATURES  ......      14 

PART  II.     STRUCTURAL  GEOLOGY. 

I.    CONSTITUTION  OF  ROCKS     . 18 

Minerals         ,~ 18 

Kinds  of  Rocks -     .      28 

II.   ROCK  MASSES,  OR  TERRANES 41 

THE  ANIMAL  AND  VEGETABLE  KINGDOMS. 

CLASSIFICATION  ...........      58 

The  Animal  Kingdom    .        .        ...        .        .        .59 

The  Vegetable  Kingdom         ....        .       '.        .      86 

GEOGRAPHICAL  DISTRIBUTION  OF  MARINE  LIFE       .        .        ,        .       91 

PART  III.     DYNAMICAL  GEOLOGY. 

I.    LIFE    .        .        .  (      .        .        ....      .        .        .        .        .        .97 

1.  Formative  Work        .  .  .        .        .  98 

2.  Protective  and  Destructive  Effects 109 


vili  CONTENTS. 

PAGE 

II.    CHEMICAL  ACTION  OF  THE  AIR  AND  WATERS  ....  Ill 

1.  Destructive  Effects Ill 

2.  Formative  Effects 116 

III.  MECHANICAL  EFFECTS  OF  THE  ATMOSPHERE    ....  118 

1.  Denudation,  Transportation,  Deposition  ....  118 

2.  Winds  as  Transporters  of  Moisture  .        .        .        .        .  123 

IV.  MECHANICAL  EFFECTS  OF  WATER 124 

1.  Fresh  Waters     . 124 

2.  The  Ocean 146 

3.  Freezing  and  Frozen  Waters     .        .        .        .        .        .157 

Summary.     Formation  of  Sedimentary  Strata       .        .        .  165 

V.   HEAT          .        .        .        .        ....        .        .        .167 

1.  Sources  of  Heat 167 

2.  Effects  of  Heat  .        .        . 172 

1.  Expansion  and  Contraction 172 

2.  Eruptions  of   Igneous  Rock,  and  Associated  Phe- 

nomena .    •    .        .        .        .        .        .        .        .  174 

3.  Metamorphism 190 

4.  Formation  of  Veins    .        .        .        .        .        .        .196 

VI.   CRUSTAL     MOVEMENTS  ;     EVOLUTION    OF     CONTINENTS    AND 

MOUNTAINS        ......         ...  203 

Evolution  of  the  Earth's  Fundamental  Features   .        .        .  206 

Structure  of  Mountain  Ranges 210 

Process  of  Formation  of  Mountain  Ranges    ....  216 

PART  IV.    HISTORICAL  GEOLOGY. 

INTRODUCTION    .                         223 

I.   ARCHAEAN  TIME 236 

II.   PALEOZOIC  TIME 242 

I.   Eopaleozoic  Section 244 

I.    Cambrian  Era 244 

II.   Lower  Silurian  Era 252 

Disturbances  at  the  Close  of  the  Lower  Silurian  Era    .  260 


CONTENTS.  ix 

PAGE 

II.  Neopaleozoic  Section 263 

I.   Upper  Silurian  Era 263 

II.   Devonian  Era         .        .        .        .        .                .  275 

III.   Carboniferous  Era          .        .        .        .                 .        .  290 

General  Observations  on  Paleozoic  Time       ....  316 

Disturbances  at  the  Close  of  Paleozoic  Time         .        .        .  325 

III.  MESOZOIC  TIME ,        .        .  330 

I.   Triassic  and  Jurassic  Eras       ......  332 

Disturbances  at  the  Close  of  the  Jurassic  Era       .        . '       .  362 

II.   Cretaceous  Era        .        . 362 

General  Observations  on  Mesozoic  Time        ....  379 

Disturbances  at  the  Close  of  Mesozoic  Time          .        .        .  383 

IV.  CENOZOIC  TIME 385 

I.   Tertiary  Era 386 

II.    Quaternary  Era 405 

1.  Glacial  Period     .        .        .        .        .        ...  406 

2.  Champlain  Period 420 

3.  Recent  Period 425 

Life  of  the  Quaternary -   .  429 

General  Observations  on  Cenozoic  Time        ....  442 

GENERAL  OBSERVATIONS  ON  GEOLOGICAL  HISTORY  .        .        .        .  444 

Length  of  Geological  Time 444 

Geographical  Progress  in  North  America       .        ....  445 

Progress  of  Life 450 

Conclusion 464 


GEOLOGY. 

ITS  AIM,   SUBJECTS,   AND  DIVISIONS. 


Aim  of  Geology.  —  Beneath  the  soil  and  waters  of  the 
earth's  surface  there  is  everywhere  a  basement  of  rocks. 
The  rocky  bluffs  forming  the  sides  of  many  valleys,  the 
ledges  about  the  tops  of  hills  and  mountains,  and  the 
cliffs  along  seashores,  are  portions  of  this  basement  ex- 
posed to  view.  Geology  is  the  science  that  studies  these 
rocks,  not  merely  to  learn  about  ore  beds,  coal,  and  build- 
ing materials,  but  primarily  to  gather  from  them  facts 
about  the  earth's  history — the  history  of  its  rocks,  fea- 
tures, and  life.  It  is  an  outdoor  science,  and  out  of  doors 
are  found  the  best  places  of  instruction  for  pupils  and 
teacher. 

Subjects  of  Study.  —  1.  Making  of  Beds  of  EocJc. — In 
most  of  the  rocky  bluffs  and  ledges  over  the  country,  the 
rocks  lie  in  successive  beds.  The  beds  differ  in  thickness 
and  in  other  ways.  They  may  be  all  sandstone,  and  show 
the  grains  of  sand  distinctly  under  a  pocket  lens.  One 
or  more  of  the  beds  may  contain  smoothly  worn  pebbles, 
with  sand  —  the  same  material  that  constitutes  a  gravel 
bed  ;  another  may  be  a  shale,  so  soft  and  fine-grained  that, 
if  ground  up  and  mixed  with  water,  it  will  make  mud  — 
suggesting  that  it  might  have  been  formed  out  of  mud. 

The  questions  arise  :  How  were  the  pebbles  rounded  ? 
How  were  the  mud,  sand,  and  gravel  distributed  in  beds  ? 
Whence  the  sand,  pebbles,  and  mud? 

1 


2  INTRODUCTION. 

At  the  foot  of  such  a  bluff  there  commonly  lie  heaps  of 
loose  sand  and  stones  derived  from  the  bluff.  The  rains, 
frost,  and  other  causes  keep  wearing  its  surface,  dropping 
grains,  and  tumbling  down  fragments ;  and  thus  the 
debris  is  formed.  If  a  stream  runs  by  the  base  of  such  a 
bluff,  the  water  when  in  rapid  flow  will  wear  away  and 
carry  off  the  material,  grinding  and  rounding  the  fallen 
fragments.  If  the  bluff  stands  on  a  seashore,  the  waves 
beating  against  its  exposed  front  will  aid  in  the  work  of 
reducing  it  to  sand,  stones,  and  mud,  for  distribution  by 
the  waters  off  the  shore  and  upon  the  beach. 

All  over  the  world  the  exposed  rocks  of  hills,  mountains, 
and  plains  are  undergoing  wear  and  decay,  and  becoming 
reduced  to  earth  and  coarser  loose  material.  And,  if  the 
whole  world  is  thus  engaged,  and  has  always  been  at  this 
work  since  rocks  were  first  exposed  to  the  action  of  the 
air  and  waters,  there  ought  to  have  been  produced  at 
all  times,  through  period  after  period,  not  only  loose 
material  enough  for  making  soil,  but  also  for  the  forma- 
tion of  vast  accumulations  of  sand  beds,  gravel  beds,  mud 
beds. 

Along  the  bottom  of  a  broad  river  valley,  either  side  of 
the  stream,  there  are  beds  of  loose  sand,  gravel,  and  clay, 
lying  in  many  alternations  parallel  with  the  surface.  Up 
or  down  the  valley,  evidence  may  usually  be  found  that 
the  flowing  waters  are  always  at  work,  but  especially  in 
flood  times,  wearing  stones  to  earth,  and  carrying  down 
stream  the  ground-up  material  for  deposition  over  the  flats 
either  side  ;  evidence,  therefore,  that  the  rivers  have  made 
the  beds  which  border  them. 

So  again,  along  seashores,  there  are  great  deposits  which 
the  waters  have  made  from  the  sand  and  pebbles  supplied 
by  the  battered  bluffs  and  from  the  sediment  which  the 
rivers  carry  to  the  ocean.  They  form  wide  sand  flats  off 
the  shores,  which  are  left  bare  by  the  retreating  tides,  and 
extensive  mud  beds  and  sand  beds  in  the  deeper  waters, 
and  beach  deposits  above  tide  level. 


INTRODUCTION.  3 

These  river-made  and  sea-made  beds  are  now  unhard- 
ened;  but  the  evidence  gathered  has  made  it  certain  that 
most  of  the  hard  rocks  are  similar  deposits  consolidated ; 
that  they  were  spread  out  in  beds  in  the  same  ways  in 
which  beds  are  now  formed  along  or  off  seashores,  in  river 
valleys,  and  in  lakes.  Nine  tenths  of  the  rocks  studied 
by  the  geologist  are  water-made  rocks.  Nearly  all  the 
older  water-made  rocks  are  of  marine  origin,  because,  in 
early  time,  the  ocean  spread  over  the  continents,  leaving 
only  islands  to  mark  their  sites.  The  continental  seas 
were  then  the  great  workers;  the  little  lands  had  only 
little  rivers. 

Again,  rocky  bluffs  often  consist  in  part  or  wholly  of 
beds  of  limestone.  Limestones  are  now  being  made  where 
the  seas  abound  in  shells  and  corals.  The  process  may  be 
studied  about  the  shores  of  Florida,  at  the  Bahamas,  and 
at  Bermuda,  as  well  as  about  many  islands  of  the  Pacific 
and  the  East  Indies.  The  process  is  now  going  on,  as  in 
ancient  time. 

In  many  beds  there  are  alternating  ridges  and  furrows, 
like  the  so-called  ripple-marks  now  often  formed  by  the 
currents  in  shallow  water  ;  or  cracks  —  though  now  tilled 
—  that  were  opened  by  the  drying  sun  in  an  exposed 
mud  flat ;  or  impressions  that  were  produced  by  the  drops 
of  a  fall  of  rain.  Such  markings  are  records  as  to  the 
origin  of  the  rocks  —  the  ripple-marks  telling  of  their  for- 
mation in  shallow  waters,  or  as  sand  flats  ;  the  mud-cracks 
showing  that  the  rock,  when  soft  mud,  was  exposed  at 
times  to  the  drying  sun  above  the  water's  surface ;  the 
raindrop  impressions  teaching  that  it  rained  in  ages  long 
past,  and  that  the  bed  so  marked  was  a  mud  flat  or  a  bed 
of  fine  wet  sand,  lying,  during  the  storm,  uncovered  by  the 
water.  Thus,  among  the  geological  records,  there  are 
facts  as  to  the  depth  of  the  waters,  and  meteorological 
records. 

2.  Excavating  Work  of  Waters.  —  Over  the  earth's  sur- 
face rivers  work,  not  merely  at  transporting  and  making 


4  INTRODUCTION. 

deposits  of  sediment,  but  also  at  excavating  channels  over 
the  land.  And  so  they  have  worked  in  the  past;  and  to 
them,  in  large  part,  the  earth  owes  its  valleys,  great  and 
small,  the  shapes  of  its  ridges,  and  the  manifold  details  of 
mountain  scenery.  Moreover,  while  doing  this  excavating 
work,  the  waters  of  the  land  have  gathered  much  of  their 
material  for  the  making  of  rocks. 

Part  of  the  work  of  water,  especially  in  later  geologi- 
cal time,  in  both  transportation  and  excavation,  has  been 
carried  on  by  water  in  the  state  of  ice,  forming  glaciers 
and  icebergs. 

3.  Fossils;  Life. — The  beds,  whether  of  sand,  mud, 
or  gravel,  or  of  limestone,  often  contain  shells,  corals, 
bones,  or  remains  of  plants  —  fossils,  as  they  are  called, 
from  the  Latin  word  fossilis,  signifying  dug  up.  The 
shells  or  bones  could  not  have  got  into  the  beds,  except 
when  the  layer  containing  them  was  forming.  They  are 
like  the  shells  in  the  mud  or  sand  of  existing  sea  bottoms 
or  sand  beaches,  and  bear  evidence  of  the  existence  of 
life,  and  make  known  what  species  were  living  in  the  seas 
when  the  bed  was  made.  The  fossils  of  the  lower  and 
upper  beds  in  the  same  bluff  often  differ,  showing  that, 
when  the  later  beds  were  in  progress,  the  old  species  had 
gone  and  new  kinds  had  come  in.  Through  the  whole 
series  of  the  earth's  rocks  new  kinds  continue  to  appear, 
and  the  old  to  disappear,  on  passing  up  from  one  level  to 
another.  Thus  a  history  of  the  life  of  the  globe,  from 
the  simplest  species  of  the  early  rocks  to  man,  has  already 
been  deciphered,  and  each  year  of  further  study  is  adding 
to  its  completeness.  The  history  of  the  earth's  life  is  the 
grandest  subject  of  geological  study. 

But  the  fossils  teach  other  lessons.  As  the  species  of 
successive  periods  differed,  the  kinds  found  in  any  rock 
are  evidence  as  to  its  age.  Again,  they  are  evidence 
whether  rocks  are  of  marine  origin  or  not ;  and  thus  they 
contribute  facts  as  to  the  earth's  early  geography.  They 
are  often  evidence,  also,  as  to  temperature  or  climate ;  for, 


INTRODUCTION.  5 

as  now,  some  species  have  required  a  warm,  and  others  a 
cool  temperature. 

4.  Mountain-making.  —  Rocks    over     large     areas     in 
many  regions  are  now  upturned  and  lifted  into  moun- 
tain ranges  hundreds  or  thousands  of  miles  long.     The 
rocks  show  by  their  position  that,  in  the  mountain-making, 
they  were  pushed  out  of  their  original  positions  by  some 
subterranean  agency.     The  origin  of  mountains  and  the 
times   of    such   upturnings   are    subjects    for   geological 
study. 

The  upturned  rocks  have  sometimes  become  crystallized, 
or  converted  into  marble,  granite,  mica  schist,  and  the 
like ;  and  such  transformations  furnish  another  subject  of 
study. 

5.  Fractures;     Veins;     Volcanoes;     Geysers.  —  Again, 
in  many  regions  the  earth's  crust  has  been  deeply  frac- 
tured.    Sometimes  mineral  veins  have  formed  in  the  fis- 
sures.    Often   melted   rock,  from   unknown   depths,  has 
come  to  the  surface  and  spread  widely  over  it,  thus  adding 
fire-made,  or  igneous,  rocks  to  those  which  are  water-made. 
Occasionally  volcanoes  have  formed  over  the  larger  fis- 
sures ;  and  in  a  few  places  geyser  regions,  like  that  of  the 
Yellowstone  Park,  have  been  left  as  residual  effects  of 
volcanic  action. 

From  the  above  explanations  it  is  obvious  that  several 
great  subjects  are  treated  under  Geology. 

(1)  The  characteristics  of  the  rocks  of  the  globe. 

(2)  The  historical  succession  in  the  formation  of  the 
rocks. 

(3)  The  origin  of  the  rocks. 

(4)  The  origin  of  rivers,  lakes,  and  seas. 

(5)  The  origin  of  mountains,  igneous   eruptions,  vol- 
canoes, and  of  fractures  in  the  earth's  crust  and  changes 
of  level. 

(6)  The  history  of  continent-making,  and  the  origin  of 
the  system  in  the  arrangement  of  the  earth's  coast  lines, 
its  mountain  chains,  and  its  island  ranges. 


6  INTRODUCTION. 

(7)  The  history  of  the  earth's  climates. 

(8)  The  history  of  life. 

In  the  study  of  these  subjects,  Geology  assumes  with 
good  reason  that  the  physical  forces  now  in  action  have 
been  the  same,  and  under  the  same  laws,  through  all  past 
time.  Whether  those  of  the  waters,  the  winds,  heat,  co- 
hesion, or  of  whatever  kind,  these  forces  have  produced 
results  through  the  ages  like  those  observed  about  us, 
with  little  difference  except  that  some  forces  must  have 
acted  with  greater,  and  others  with  less,  intensity  in  early 
geological  time.  Existing  nature,  therefore,  affords  the 
means  of  interpreting  the  geological  records. 

Divisions  of  the  Science.  —  The  divisions  of  the  science 
here  adopted  are  .the  following :  — 

1.  Physiographic   Geology.  —  Treating   of    the   earth's 
physical  features ;  that  is,  of  the  system  in  the  exterior 
features  of  the  earth.     This  department  properly  includes 
also  the  system  of  movements  in  the  water  and  atmos- 
phere, and  the  system  in  the  earth's  climates,  and  in  the 
other  physical  agencies  or  conditions  of  the  sphere. 

2.  Structural  Geology.  —  Treating  of  the  rocks  of  the 
globe,  their  kinds,  structure,  and  arrangement  in  beds  or 
otherwise. 

3.  Dynamical  Geology.  — Treating  of  the  causes,  or  the 
methods,  by  which  all  the  earth's  changes  were  brought 
about,   including   the    making   of    continents,    of    ocean 
basins,  of  rocks,  of  mountains,  of  valleys ;  the  causes  of 
all  variations  in  climate,  and  of  all  changes  in  the  earth's 
features,  and  of  the  system  in  the  progress  of  life.     The 
word  dynamical  is  from  the  Greek  Svvafus,  power  or  force. 

4.  Historical    Geology.  —  Treating    of     the    successive 
events  in  the  history  of  the  rocks,  and  of  the  continents, 
oceans,  mountains,  valleys,  coast  lines,  climates,  and  life. 


PAET  L  —  PHYSIOGRAPHIC  GEOLOGY. 


I.    GENERAL   FEATURES   OF   THE   EARTH'S 
SURFACE. 

Size  and  Form.  —  The  earth  has  a  circumference  of 
about  25,000  (24,899)  miles.  Its  form  is  that  of  a  sphere 
flattened  at  the  poles,  the  equatorial  diameter  (7926  miles) 
being  about  26J  miles  greater  than  the  polar  diameter. 

Regions  of  Depression  and  Elevation.  —  About  eight 
elevenths  of  the  earth's  surface,  or  144,000,000  square 
miles,  is  depressed  below  the  rest,  and  occupied  by  salt 
water.  This  sunken  part  of  the  crust  is  called  the  oceanic 
basin,  and  the  large  areas  of  land  are  called  the  continents 
or  continental  plateaus.  The  area  of  the  continents  and 
islands  is  about  52,745,000  square  miles. 

Arrangement  of  Oceans  and  Continents.  —  Nearly  three 
fourths  of  the  area  of  the  continental  plateaus  is  situ- 
ated in  the  northern  hemisphere,  and  very  nearly  three 
fifths  of  the  oceanic  basin  in  the  southern  hemisphere. 
The  dry  land,  as  shown  in  the  map,  Fig.  1,  may  be 
said  to  be  grouped  about  the  North  Pole,  and  to  stretch 
southward  in  two  masses,  an  Oriental,  including  Eu- 
rope, Asia,  Africa,  and  Australasia,  and  an  Occidental, 
including  North  and  South  America.  The  ocean  is 
gathered  in  a  similar  manner  about  the  South  Pole,  and 
extends  northward  in  two  broad  areas  separating  the 
Occident  and  Orient,  namely,  the  Atlantic  and  Pacific 
Oceans,  and  also  in  a  third,  the  Indian  Ocean,  separating 

7 


8 


PHYSIOGRAPHIC   GEOLOGY. 


the  southern  prolongations  of  the  Orient,  namely,  Africa 
and  Australasia.  The  Orient  is  made,  by  this  arrange- 
ment, to  have  two  southern  prolongations,  while  the  Occi- 
dent, or  America,  has  but  one.  This  double  feature  of 
the  Orient  accords  with  its  great  breadth ;  for  it  averages 
6000  miles  from  east  to  west,  which  is  far  more  than 
twice  the  mean  breadth  of  the  Occident  (2200  miles). 
The  inequality  of  the  two  continental  masses  has  its 
parallel  in  the  inequality  of  the  Pacific  and  Atlantic 
oceans ;  for  the  former  (6000  miles  broad)  is  more  than 
double  the  average  breadth  of  the  latter  (2800  miles). 

FIG.  1. 


Land  hemisphere  and  water  hemisphere. 

The  northern  portion  of  the  Orient,  or  Europe  and  Asia 
combined,  makes  one  continental  area,  Eurasia;  its  gen- 
eral course  is  east  and  west.  The  northern  portion  of  the 
Occident,  North  America,  is  elongated  from  north  to  south. 

Depth  of  Oceans  and  Height  of  Continents.  — The  mean 
depth  of  the  oceanic  depression  is  about  14,000  feet ; 
and  the  mean  height  of  the  land  (according  to  Murray) 
2252  feet.  The  greatest  depth  reached  by  soundings 
(south  of  the  Friendly  Islands)  is  30,930  feet ;  the  great- 
est height  on  the  land  (Mt.  Everest  of  the  Himalayas)  is 
29,000  feet ;  hence  the  interval  between  the  extremes  of 


THE  EARTH'S  FEATURES.  9 

altitude  and  depression  is  over  eleven  miles.  If  the  con- 
tinental plateaus  and  the  floor  of  the  ocean  were  graded 
to  a  common  level,  the  ocean  would  still  have  a  depth  of 
about  10,000  feet.  The  mean  height  of  Europe  is  (accord- 
ing to  Murray)  939  feet ;  Asia,  3189  feet ;  Africa,  2021 
feet ;  Australia,  805  feet ;  North  America,  1888  feet ; 
South  America,  2078  feet.  The  mean  depths  of  the  great 
oceans  are  :  of  the  North  Atlantic,  15,000  feet ;  North 
Pacific,  16,000  feet;  South  Atlantic  and  South  Pacific 
(and  probably  the  Indian  Ocean),  about  13,000  feet. 

The  Form  of  the  Ocean* s  Bed.  —  Fig.  2  shows  the  gen- 
eral form  of  the  ocean's  bed  beneath  the  larger  oceans. 
From  north  to  south,  along  the  middle  of  the  Atlantic, 
there  is  a  wide  zigzag  ridge  or  plateau,  conforming  nearly 
in  trend  to  the  American  coast.  It  lies  at  a  depth  of  6000 
to  12,000  feet,  while  on  either  side  the  bottom  slopes  away 
to  depths  mostly  between  15,000  and  20,000  feet.  In  the 
area  of  4000  fathoms  and  over,  situated  north  of  the 
island  of  Puerto  Rico,  the  United  States  Coast  Survey 
steamer  Blake  found,  in  1883,  a  depth  of  27,366  feet. 
This  greatest  depth,  and  large  areas  of  deep  water,  exist 
in  the  western  part  of  the  ocean.  In  the  Pacific  Ocean,  a 
shallow  area  extends,  with  little  interruption,  from  the 
Malay  Archipelago  southeastward  beyond  the  Paumotu 
Islands,  and  thence  northeastward  to  the  Isthmus  of 
Panama,  southeastward  to  Patagonia,  and  southward  to 
the  Antarctic.  The  deepest  parts  of  this  ocean  also  are 
in  its  western  half.  One  deep  area  is  east  of  Japan;  another, 
south  of  the  Ladrones ;  others,  near  the  Friendly  Islands. 
Northward  in  the  northern  hemisphere  the  ocean  shallows 
rapidly.  The  depth  in  Bering  Strait  is  not  over  150  feet ; 
and  between  Great  Britain  and  Iceland  it  does  not  exceed 
6000  feet,  and  is  mostly  under  3000  feet. 

The  ocean's  bottom  has  no  steep  ridges  like  those  of 
ordinary  mountain  scenery.  But  broad  elevations  exist 
in  some  parts,  as  found  in  the  soundings  of  the  Tuscarora 
between  the  Hawaiian  Islands  and  Japan.  Besides  these, 


Fi 


160 


190 


Longitude  120  East  160 


120  West 


0-100  fathoms 


100-2000  fathoms  JJ  2000- 

BATHYMETKLC   CHJ? 


0  fathoms  |  3000-4000  fathoms       |H  4000  fathoms  and  over 

,T   OF   THE   OCEANS 


12  PHYSIOGKAPHIC   GEOLOGY. 

there  are  many  mountain  ranges  rising  somewhat  abruptly 
from  the  depths,  having  the  islands  of  the  ocean  as  their 
summits,  which  rival  in  length  those  of  the  continents. 
The  Hawaiian  range,  if  the  coral  islands  in  the  line 
of  the  volcanic  islands  are  included  (see  Fig.  2),  has  a 
length  of  2000  miles ;  and  it  rises  steeply  from  depths  of 
15,000  to  18,000  feet.  The  mountains  of  Hawaii  have  a 
height  above  the  ocean  of  nearly  14,000  feet,  and  a  depth 
of  17,000  feet  was  found  but  50  miles  south  of  the  island, 
thus  making  the  whole  height  nearly  31,000  feet.  The 
islands  of  the  tropical  Pacific  make  together  an  island 
chain  about  5000  miles  long ;  and  they  are  the  tops  of  a 
mountain  chain  of  this  great  length. 

True  Outline  of  the  Oceanic  Depression.  —  Along  the 
oceanic  borders,  the  sea  is  often,  for  a  long  distance  out, 
quite  shallow,  because  the  continents  continue  on  under 
water  with  a  nearly  level  surface ;  then  comes,  usually 
at  a  depth  of  about  100  fathoms,  or  600  feet,  a  rather 
sudden  slope  to  the  deep  bed  of  the  ocean.  This  is  the 
case  off  the  eastern  coast  of  the  United  States,  east  and 
south  of  New  England.  Off  New  Jersey,  as  is  shown  by 
Fig.  3,  the  deep  water  begins  along  a  line  about  80  miles 
from  the  shore  ;  off  Virginia  this  line  is  50  to  60  miles 
at  sea ;  and  thus  it  gradually  approaches  the  coast  to  the 
southward:  while  to  the  northward  it  continues  80  to  100 
miles  off  from  the  New  England  coast,  and  passes  far  out- 
side of  Nova  Scotia  and  Newfoundland  (see  Fig.  2).  The 
slope  of  the  bottom,  for  the  80  miles  off  New  Jersey,  is 
only  1  foot  in  700  feet.  The  true  boundary  between 
the  continental  plateau  and  the  oceanic  depression  is  the 
commencement  of  the  abrupt  slope.  The  same  abrupt 
slope  near  the  100-fathom  line  exists  in  the  Gulf  of 
Mexico.  The  British  Islands  are  situated  on  a  submerged 
portion  of  the  European  continent,  and  are  essentially  a 
part  of  that  continent,  the  limit  of  the  oceanic  basin  — 
the  100-fathom  line  —  being  50  to  100  miles  outside  of 
Scotland  and  Ireland,  and  extending  south  around  the 


THE   EARTH  S   FEATURES. 


13 


Bay  of  Biscay.  West  of  the  English  Channel  the  depth 
increases,  in  a  distance  of  only  ten  miles,  from  100  fathoms 
to  2000.  New  Guinea  is  in  a  similar  way  proved  to  be  a 
part  of  Australia.  Such  facts  occur  on  most  coasts  ;  and 
they  teach  that  the  oceanic  depression  is  generally  separated 
from  the  continental  plateaus  by  a  well-defined  outline. 

FIG.  3. 


Bathymetric  chart  of  region  south  of  Long  Island. 

Surfaces  of  the  Continents.  —  The  surface  of  a  conti- 
nent comprises  (1)  plains  or  lowlands,  (2)  plateaus  or 
table-lands,  and  (3)  mountain  ridges.  The  mountain  ridges 
may  rise  either  from  the  lowlands  or  the  plateaus.  The 
plateaus  are  large  areas  of  approximately  level  surface  at 
an  altitude  of  a  thousand  feet  or  more  above  the  sea. 
They  are  often  parts  of  the  great  mountain  chains,  lying 


14  PHYSIOGRAPHIC   GEOLOGY. 

between  the  ridges,  or  forming  the  mountain  mass  out 
of  which  the  ridges  rise.  For  example,  the  regions  of 
northern  and  southern  New  York  are  plateaus  (the 
former  averaging  1500  feet  in  height,  the  latter  2000  feet) 
situated  on  the  western  borders  of  the  Appalachian  chain; 
and  the  same  is  true  of  the  Cumberland  table-land  in 
Tennessee.  Between  the  Sierra  Nevada  and  the  Wasatch, 
there  is  a  plateau  of  vast  extent,  called  the  Great  Basin, 
having  the  Great  Salt  Lake  in  its  northeastern  portion ; 
its  height  above  the  sea  averages  4000  feet;  the  Hum- 
boldt  Mountains  and  other  high  ranges  rise  out  of  it.  It 
continues  northward  into  British  America  and  southward 
into  Mexico.  The  eastern  part  of  New  Mexico,  with  the 
western  part  of  Texas,  is  a  plateau  of  about  the  same  ele- 
vation, called  the  Llano  Estacado.  The  Desert  of  Gobi, 
between  the  Altai  and  the  Kuen-Lun  range,  is  a  desert 
plateau  about  4000  feet  high,  while  the  plateau  of  Tibet, 
between  the  Kuen-Lun  range  and  the  Himalayas,  is 
11,500  to  13,000  feet  above  the  sea.  Persia  and  Armenia 
constitute  another  plateau.  These  examples  are  sufficient 
to  explain  the  use  of  the  term. 

II.    SYSTEM   IN   THE  EARTH'S  FEATURES. 

General  Relief  of  the  Continents.  —  The  continents  are 
constructed  on  a  common  model :  they  have  high  bor- 
ders and  a  low  center,  and  are,  accordingly,  basin-shaped. 
North  America  has  the  Appalachians  on  the  eastern  border, 
the  Cordillera  on  the  west,  and  between  these  the  low 
Mississippi  basin.  Fig.  4  illustrates  this  form  of  the  con- 
tinent. In  the  section,  b  represents  the  Rocky  Mountain 
chain  on  the  west,  with  its  lines  of  ridges  at  summit ;  a, 
the  Sierra  chain  (including  the  Sierra  Nevada  and  Cascade 
Range),  near  the  Pacific  coast ;  <?,  the  Mississippi  basin ; 
c?,  the  Appalachian  chain  on  the  east. 

South  America,  in  a  similar  manner,  has  the  Andes  on 
the  west,  the  Brazilian  Mountains  on  the,  east,  and  other 


THE  EARTH'S  FEATURES. 


15 


heights  along  the  north,  with  the  low  region  of  the  Ama- 
zon and  La  Plata  making  up  the  larger  part  of  the  great 
interior.  Fig.  5  is  a  transverse  section  from  west  to 
east,  showing  the  Andes  at  a,  and  the  Brazilian  Moun- 
tains at  b.  In  these  sections  the  height  as  compared  with 
the  breadth  is  necessarily  much  exaggerated. 

In  the  Orient  there  are  mountains  on  the  Pacific  side, 
others  on  the  Atlantic ;  and,  again,  the  Himalayas,  on  the 
south,  face  the  Indian  Ocean,  and  the  Altai  Mountains 


FIG.  4. 


Profile  of  North  America. 

face  the  Arctic  seas.  Between  the  Himalayas  (or  rather 
the  Kuen-Lun  Mountains,  which  are  just  north)  and  the 
Altai,  lies  the  plateau  of  Gobi,  which  is  low  compared  with 
the  inclosing  mountains ;  and  farther  west  there  are  the 
lowlands  of  the  Caspian  and  Aral,  the  Caspian  lying  even 
below  the  level  of  the  ocean.  The  Urals  divide  the  6000 
miles  of  breadth  into  two  parts,  and  so  give  Europe  some 

FIG.  5. 


Profile  of  South  America. 

title  to  its  designation  as  a  separate  continent.  West 
of  their  meridian  there  are  again  extensive  lowlands  over 
middle  and  southern  European  Russia.  In  Africa  there 
are  mountains  on  the  eastern  border,  and  on  the  western 
border  south  of  Guinea ;  there  are  also  the  Atlas  Moun- 
tains along  the  Mediterranean,  and  the  Kong  Mountains 
along  the  Guinea  coast ;  and  the  interior  is  relatively  low, 
although  mostly  1000  to  2000  feet  in  elevation.  In  Aus- 
tralia, also,  there  are  highlands  on  the  eastern  and  western 
borders,  and  the  interior  is  low.  All  the  continents  are, 
therefore,  constructed  on  the  basin-like  model. 


16  PHYSIOGRAPHIC    GEOLOGY. 

The  Greater  Mountains  border  the  Greater  Ocean. — 
There  is  a  second  great  truth  with  regard  to  the  conti- 
nental reliefs  :  the  highest  border  faces  the  largest  ocean. 
Each  of  the  continents  sustains  the  truth  announced. 
North  America  has  its  great  mountains,  the  Cordillera,  on 
the  side  of  the  great  ocean,  the  Pacific ;  and  its  small 
mountains,  the  Appalachians,  on  the  side  of  the  small 
ocean.  South  America,  also,  has  its  highest  border  on  the 
west.  The  Orient  has  high  ranges  of  mountains  on  the  east, 
or  the  Pacific  side,  and  lower  ranges,  as  those  of  Norway 
and  other  parts  of  Europe,  on  the  west ;  and  the  Hima- 
layas face  the  great  Indian  Ocean,  while  the  smaller  Altai 
range  faces  the  small  Northern  Ocean.  In  Africa,  the 
mountains  on  the  side  of  the  Indian  Ocean  are  higher 
than  those  on  that  of  the  Atlantic.  In  Australia  the 
highest  border  is  on  the  Pacific  side  ;  for  the  South  Pacific 
fronting  east  Australia,  is  greater  than  the  Indian  Ocean 
fronting  west  Australia.  Hence  the  basin-like  shape  be- 
fore illustrated  is  that  of  a  basin  with  one  border  much 
higher  than  the  other  ;  and  with  the  highest  border  on 
the  side  of  the  largest  ocean. 

The  features  described  have  a  vast  influence  in  adapting 
the  continents  for  man.  America  has  its  highest  border 
in  the  far  west,  with  all  its  great  plains  and  great  rivers 
inclined  toward  the  Atlantic;  for,  through  the  Gulf  of 
Mexico,  the  whole  interior,  as  well  as  the  eastern  border, 
has  its  natural  outlet  eastward.  The  Orient,  instead  of 
rising  into  Himalayas  on  the  Atlantic  border,  has  its  great 
heights  in  the  remote  east ;  and  its  vast  plains,  even  those 
of  Central  Asia,  have  their  natural  outlet  westward,  over 
Europe  and  through  the  Mediterranean,  or  toward  the 
same  Atlantic  Ocean.  Thus,  as  Professor  Guyot  has  said, 
the  vast  regions  of  the  world,  which  are  best  fitted  for 
man,  by  their  climate  and  productions,  are  combined  into 
one  great  arena  for  the  progress  of  civilization. 


PART   II.— STRUCTURAL   GEOLOGY. 


THE  term  rock,  in  geology,  is  applied  to  all  natural 
formations  of  mineral  material,  whether  consolidated,  like 
sandstones  and  slates,  or  unconsolidated,  like  sand  and 
gravel.  All  sandstones  were  once  beds  of  loose  sand ; 
and  there  is  every  shade  of  gradation,  from  the  hardest 
sandstone  to  the  softest  sand  bed ;  so  that  it  is  impossible 
to  draw  a  line  between  the  consolidated  and  the  unconsoli- 
dated. Geology  does  not  attempt  to  draw  the  line,  re- 
garding consolidation  as  an  accident  in  the  history  of  the 
earth's  beds  or  deposits  —  an  accident  that  probably  hap- 
pened to  only  a  small  part  of  the  sand  beds  and  mud 
beds  that  have  existed,  and  yet  to  enough  of  them  in 
each  period  for  the  preservation  of  the  wonderfully  varied 
records  that  are  the  materials  of  geological  science. 

Rocks  may  be  studied  simply  as  rocks,  —  that  is,  with 
reference  to  their  composition,  —  and  collections  may  be 
made  containing  specimens  of  their  various  kinds.  Again, 
they  may  be  studied  as  rock  masses  spread  out  over  the 
earth  and  forming  the  earth's  crust ;  and,  with  this  in 
view,  the  condition,  structure,  and  arrangement  of  the 
great  rock  masses,  called  terranes,  would  come  up  for  con- 
sideration. The  two  subjects  under  Structural  Geology 
are,  therefore :  — 

1.  THE  CONSTITUTION  OF  ROCKS. 

2.  THE  CONDITION,  STRUCTURE,  AND  ARRANGEMENT 

OF  ROCK  MASSES,  OR  TERRANES. 

17 


18  STRUCTURAL   GEOLOGY. 

I.    CONSTITUTION   OF   ROCKS. 
Minerals. 

Rocks  are  generally  heterogeneous,  being  composed  of 
grains  or  particles  of  different  materials.  The  separate 
grains  or  particles,  which  are  homogeneous  or  nearly 
so,  having  a  definite  chemical  constitution,  are  called 
minerals.  The  minerals  which  constitute  the  principal 
ingredients  of  the  common  rocks  are  included  in  three 
groups :  — 

1.  SILICA,  or  silicon  dioxide. 

2.  SILICATES,  or  compounds  of  silicon  and  oxygen  with 
other  elements. 

3.  CARBONATES,  or  compounds  of  carbon  and  oxygen 
with  other  elements. 

Besides  these,  three  other  groups  of  minerals  should 
here  be  mentioned,  as  sometimes  constituting  rock  masses, 
and  including  materials  of  special  importance  :  — 

4.  CARBON  AND  ITS  COMPOUNDS  (other  than  carbo- 
nates). 

5.  CHLORIDES. 

6.  IRON  ORES. 

1.  SILICA. 

Silica,  or  silicon  dioxide  (SiO2),  in  its  most  common 
molecular   arrangement,   constitutes   the   mineral   quartz, 
which  far  exceeds  all  other  minerals  in 
abundance.     It  is  one  of  the  hardest  of 
i\   common  minerals ;  does  not  melt  before 
the   blowpipe,  and  does  not  dissolve  in 
water,  or  in  the  ordinary  acids. 

It  is  often  seen  in  crystals  like  Figs. 
6,  7,  though  generally  occurring  in  mas- 
sive forms,  or  in  grains  or  pebbles.      It  is  distinguished 
ordinarily  by  its  glassy  aspect,  whitish  or  grayish  color, 


CONSTITUTION   OF   ROCKS.  19 

and  an  absence  of  all  tendency  to  break  with  a  bright  even 
surface  of  fracture  (a  quality  possessed  by  many  crystals, 
called  cleavage).  Although  usually  nearly  colorless  or 
white,  it  is  often  reddish,  yellowish,  brownish  (especially 
smoky  brown),  and  even  black;  and  the  luster  is  some- 
times very  dull,  as  in  chalcedony,  flint,  and  jasper.  The 
sands  and  pebbles  of  the  seashores  and  gravel  beds  are 
mostly  quartz ;  because  quartz  resists  the  wearing  action 
of  waters  better  than  any  other  common  mineral.  For 
the  same  reason,  most  sandstones  and  conglomerates  con- 
sist mainly  of  quartz. 

The  hardness  (on  account  of  which  it  scratches  glass 
easily),  infusibility,  insolubility  in  acids,  and  absence  of 
cleavage,  are  the  characters  that  serve  to  distinguish 
quartz  from  the  other  ingredients  of  rocks. 

But,  though  quartz  is  so  refractory,  it  easily  fuses  into 
glass  when  mixed  with  potash,  soda,  lime,  or  an  oxide  of 
iron.  Ordinary  glass  is  made  by  mixing  powdered  quartz 
with  soda  and  sometimes  lime,  and  subjecting  the  mixture 
to  a  high  heat. 

Silica  exists  also  in  a  different  molecular  state,  in  which 
it  is  called  opal.  Opal,  a  beautiful  gem  in  some  of  its 
varieties,  does  not  occur  crystallized,  has  a  little  less  hard- 
ness than  quartz,  and  is  more  easily  soluble  in  a  heated 
alkaline  solution.  The  silica  secreted  by  some  minute 
plants,  as  Diatoms,  and  by  Sponges  and  Radiolarians 
among  animals,  is  opal ;  and  in  many  places  large  beds  of 
the  minute  shells  and  spicules  are  formed  by  the  growth 
and  death  of  the  above-mentioned  organisms  (see  page 
106). 

2.  SILICATES. 

Most  of  the  common  rock-making  minerals  are  silicates  ; 
that  is,  combinations  of  silicon  and  oxygen  with  certain 
basic  elements,  as  aluminium,  magnesium,  calcium,  potas- 
sium, sodium,  iron,  and  a  few  otliers. 

The  silicates  which  contain  no  metal  except  aluminium 


20  STRUCTURAL  GEOLOGY. 

are  infusible  as  well  as  very  hard.  But  those  which  con- 
tain one  or  more  of  the  other  metals  mentioned  are  with 
few  exceptions  fusible. 

The  following  are  the  most  common  of  these  silicates  :  — 

1.  Feldspar.  —  The  feldspars  are  silicates  of  aluminium 
with  one  or  more  of  the  metals  potassium,  sodium,  and 
calcium.     They  are  hard  enough  to  scratch  glass,  but  less 
hard  than  quartz.    They  break  easily,  or  have  cleavage,  in 
two  directions,  and  the  two  lustrous  cleavage  surfaces  meet 
nearly  or  quite  at  a  right  angle.     The  color  is  usually 
white  or  flesh-red,  rarely  dark  brown  or  greenish.     The 
specific  gravity  is  2.4  to  2.7. 

The  most  common  kind  is  a  potash  feldspar,  affording 
on  analysis  silica,  alumina,  and  potash,  and  is  called  ortho- 
clase  ;  another,  named  albite,  from  its  usual  white  color,  is 
a  soda  feldspar ;  others,  as  oligoclase,  andesine,  and  labra- 
dorite,  are  soda-lime  feldspars. 

2.  Mica.  —  Mica  is  a  silicate  of  aluminium  and  potas- 
sium, but  some  kinds  of  mica  contain  also  magnesium  and 
iron.     Mica  cleaves  easily  into  tough  leaves,  thinner  than 
the  thinnest  paper,  and  somewhat  elastic ;   it  fuses  with 
great  difficulty;  hence  its  common  use  in  lanterns  and  doors 
of  stoves.     Its  most  common  colors  are  whitish,  brownish, 
and  black.     The  most  common  kind  of  mica  has  a  light 
color,  and  is  called  muscovite,  from  its  old  name,  Muscovy 
glass ;    another,  usually  black  in  color,    is  called  biotite. 
Some  micas  are  hydrous  ;  that  is,  they  contain  water ;  and 
these  hydromicas,  as  they  are  called,  are  pearly  in  luster, 
feel  a  little  soapy,  and  are  sometimes  mistaken  for  talc. 

The  minerals,  quartz,  feldspar,  and  mica,  are  the  con- 
stituents of  granite ;  and  they  may  be  distinguished  in  it 
as  follows :  the  grains  of  quartz,  by  their  glassy  luster, 
gray  color,  and  want  of  cleavage ;  the  grains  of  feldspar, 
by  their  shining  cleavage,  as  is  well  seen  when  a  surface 
of  fracture  is  held  up  to  the  sunlight ;  the  grains  of  mica, 
by  their  very  easy  cleavage  by  means  of  the  point  of  a 
knife  blade  into  thin  elastic  leaves. 


CONSTITUTION   OF  KOCKS.  21 

3.  Hornblende  and  Pyroxene.  —  Hornblende  and  pyrox- 
ene are  silicates  of  magnesium,  calcium,  and  iron,  alumin- 
ium not  being  an  essential  constituent,  and,  when  present, 
always  in  small  amount.    The  most  common  variety  of  each 
of  these  minerals,  occurring  as  a  principal  constituent  of 
rocks,  is  black,  or  greenish  black,  and  2.9  to  3.5  in  specific 
gravity ;  but  white  and  light  green  varieties  also  are  com- 
mon.    They  are  somewhat  inferior  to  feldspar  in  hard- 
ness;   unlike  mica,   they   are   brittle.      The   crystals  or 
crystalline  grains  have  two  equally   lustrous  cleavages. 
In  hornblende,  the  angle  between  the  two  is  about  124° ; 
in  pyroxene,  about  87°.      Hornblende  is  often  in  long, 
slender  crystallizations,  and  asbestus  is  a  very  fine  fibrous 
variety  of  it,  sometimes  like  wool.     Both  hornblende  and 
pyroxene  make  hard  and  tough  rocks.      Pyroxene  is  a 
constituent  of  some  of  the  most  common  igneous  rocks. 

4.  Chrysolite.  —  A   silicate   of   magnesium   with   some 
iron.     It  is  generally  of  an  olive-green  color,  and  occurs 
in  many  igneous  rocks  in  disseminated  grains  or  crystals, 
looking  much  like  bits  of  green  bottle  glass. 

5.  Chlorite.  —  A  silicate  of  magnesium,  aluminium,  and 
iron,  containing  generally  12  per  cent  or  more  of  water. 
It  resembles  black  mica  in  its  crystallization  and  cleavage ; 
but  its  folia  are  not  elastic,  its  color  is  usually  dark  green, 
and  it  feels  a  little  greasy.     It  is  often  finely  granular. 

6.  Talc  ;  Serpentine.  —  Talc  and  serpentine  are  hydrous 
silicates  of  magnesium  ;  that  is,  silicates  containing  water. 
They  both  have  a  greasy  feel  —  especially  talc.     Talc  is 
very  soft,  so  soft  that  it  does  not  feel  gritty  to  the  teeth. 
It  is  often  in  foliated  plates  or  masses  like  mica ;  but  the 
folia,  or  leaves,  though  separating  rather  easily,  and  flex- 
ible,   are    not   elastic.     The   usual   color   is   pale   green. 
Soapstone,  or  steatite,  is  a  massive  variety   of  talc,  of 
whitish,  grayish,  or  greenish  color. 

Serpentine  contains  much  water  (about  14  per  cent). 
It  is  usually  a  dark  green  massive  mineral  or  rock,  of 
smooth  fracture,  and  soft  enough  to  be  cut  with  a  knife. 


STRUCTURAL  GEOLOGY. 


FIG.  8. 


7.  The  following  minerals  occur  distributed  in  crystals 
through  many  crystalline  rocks,  though  rarely  forming 
the  principal  constituents  of  rocks :  — 

Garnet.  —  The  most  common  varieties  are  silicates  of 
aluminium,  with  iron,  calcium,  or  magnesium.  They  occur 
often  in  dark  red,  brownish,  or  black  crystals  of  12  or  24 
sides  (dodecahedrons  or  trapezohedrons).  The  first  of 

these  forms  is  represented  in  Fig. 
8,  showing  garnets  distributed 
through  a  mica  schist. 

Tourmaline  contains,  besides  sili- 
con and  oxygen,  aluminium,  mag- 
nesium, iron,  boron,  and  fluorine. 
It  occurs  generally  (Fig.  9)  in 
crystals  which  are  prisms  of  3,  6, 
9,  or  12  sides ;  the  most  common  color  is  black,  but  it  is 
sometimes  blue-black,  brown,  green,  or  red. 

Andalusite  is  simply  an  aluminium  silicate,  and  hence  is 
infusible.  It  is  found  in  imbedded  crystals  in  clay  slate, 
and  sometimes  in  mica  schist ;  the  form  is  nearly  a  square 
prism.  The  interior  of  the  crystals  is  very  frequently 


Garnet. 


FIG.  9. 


FIG.  10. 


Tourmaline. 


Andalusite. 


black  or  grayish  black  at  the  center  and  angles  (Fig.  10), 
while  the  rest  is  nearly  white ;  and  this  variety  is  called 
macle,  or  chiastolite. 

Cyanite  has  the  same  composition  as  the  preceding,  and 
like  it  is  infusible.  It  usually  occurs  in  mica  schist  or 
gneiss,  in  thin,  bladelike,  pale  blue  crystals. 


CONSTITUTION   OF  HOCKS. 


23 


Staurolite.  —  Related  to  the  last  two  minerals,  and  in- 
fusible ;  but  it  contains  some  iron.  Its  crystals  are  stout 
prisms  of  about  129°,  of  brown  or  brownish  black  color ; 
they  often  have  the  form  of  a  cross,  whence  the  name,  from 
o-ray/xfr,  a  cross. 

3.  CARBONATES. 

1.  Calcite,  or  Calcium  carbonate  (CaCO3).  —  The  ma- 
terial of  limestone  and  marble.  It  crystallizes  in  many 
forms,  a  few  of  which  are  represented  in  Figs.  11  and  12. 
It  cleaves  easily  in  three  directions  with  bright  surfaces, 
as  may  be  seen  on  examining  even  the  grains  of  a  fine 
white  marble.  Its  colors  are  various.  It  is  so  soft  as 
to  be  easily  scratched  with  a  knife ;  dissolves  in  diluted 


Calcite. 


Calcite. 


acid  (hydrochloric)  with  effervescence,  that  is,  with  an 
escape  of  carbonic  acid  gas  (CO2);  and,  when  heated  (as 
in  a  limekiln  or  before  the  blowpipe),  it  burns  to  quick- 
lime without  melting.  By  its  effervescence  with  acids  it 
differs  from  all  the  minerals  before  mentioned. 

2.  Dolomite,  Calcium-magnesium  carbonate  (CaMgC2O6), 
differs  from  calcite  in  containing  magnesium  in  place  of 
part  of  the  calcium.  Very  much  of  limestone  is  magnesian 
limestone.  It  closely  resembles  ordinary  limestone,  but 
may  be  distinguished  by  its  effervescing  scarcely  at  all 
with  acid  unless  heat  be  applied. 

For  iron  carbonate  (siderite)  see  page  27. 


24  STRUCTURAL  GEOLOGY. 

4.  CARBON  AND  ITS  COMPOUNDS  (OTHER  THAN  CARBONATES). 

Carbon  occurs  pure  among  minerals  only  in  diamond 
and  graphite.  It  is  the  chief  element  in  mineral  coal,  but 
is  combined  in  it  with  more  or  less  of  hydrogen  and 
oxygen,  and  also  some  nitrogen.  Charcoal,  the  carlo  of 
the  Romans,  is  nearly  all  carbon. 

Carbon  occurs  in  the  atmosphere  in  the  form  of  carbon 
dioxide,  or  carbonic  acid  (CO2).  This  gas  constitutes 
about  3  out  of  10,000  parts  of  the  atmosphere,  and  is 
carried  from  tha  atmosphere  to  the  earth  by  the  rains.  It 
is  formed  in  the  combustion  of  wood,  -the  combustion  con- 
sisting in  the  combination  of  oxj^gen  with  the  constituents 
of  the  wood.  It  is  also  given  out  in  the  respiration  of 
animals,  the  processes  of  life  in  animals  being  carried  for- 
ward through  a  sort  of  combustion,  or  a  similar  combina- 
tion of  oxygen  with  the  materials  of  the  tissues. 

Aside  from  its  occurrence  in  the  carbonates,  the  chief 
form  in  which  carbon  occurs  as  a  rock  material  is  that  of 
mineral  coal. 

1.  Diamond  and  Graphite. — These  are  both  pure  carbon, 
but  in  different  molecular  states ;  the  former,  the  hardest 
of  minerals,  crystallizing  in  octahedral  and  related  forms ; 
the  latter,  one  of  the  softest,  crystallizing  in  hexagonal 
plates,  with  nearly  the  easy  cleavage  of  mica,  and  with 
metallic  luster.     Graphite    is  also  called  plumbago  and 
black  lead,  and  is  the   material  of   the   misnamed  lead 
pencils.      It   occurs   in   crystalline   rocks   in   scales   and 
masses,  and  is  ground  up  and  subjected  to  pressure  to 
prepare  it  for  making  pencils. 

2.  Mineral  Coal.  —  Mineral  coal  is  not  a  true  mineral, 
being  not  a  definite  chemical  compound,  but  a  mixture  of 
various  compounds  of  carbon  with  hydrogen  and  oxygen. 
It  constitutes  beds  in  various  rock  formations,  and  has 
been  formed  from  wood  or  some  kind  of  vegetable  mate- 
rial.    There  are  three  prominent  kinds,  differing  in  the 
amount  of  oxygen  and  hydrogen  that  is  present  with  the 


CONSTITUTION   OF   ROCKS.  25 

chief  ingredient  carbon,  and  consequently  in  the  amount 
of  inflammable  gas  given  out  in  burning.  This  gas  con- 
sists chiefly  of  carbon  and  hydrogen,  and  is  essentially  the 
same  as  the  gas  used  in  illumination. 

1.  Anthracite  contains   generally  over  85  per  cent  of 
carbon.     It  yields  little  that  is  volatile,  and  burns  with  a 
feeble  blue  flame. 

2.  Bituminous  coal  has  less  hardness  and  luster  than 
anthracite,  contains  usually  65  to  85  per  cent  of  carbon, 
and  gives  out  on  heating  20  to  50  per  cent  of  volatile 
matter.     It  therefore  burns  with  a  bright  yellow  flame. 
When  heated,  it  will   yield   illuminating   gas,  and   also 
mineral  oil.     Cannel  coal  is  a  compact   bituminous  coal 
having  a  feeble  luster ;  it  often  yields  40  to  50  per  cent 
of  volatile  matter,  and  is  an  available  source  of  mineral 
oil.     Bituminous  coal  is  called  caking  coal  when  it  softens 
in  the  fire  and  cakes  at  the  surface,  so  that  a  fire  made  of 
it  requires  poking  to  make  it  burn  freely ;    non-caking 
kinds  have  not  this  quality,  and  hence  are  preferable  for 
fuel. 

3.  Brown  coal  differs  from  bituminous  coal  in  yield- 
ing a  brownish  black  powder,  and  in  containing   much 
more  oxygen  (20  to  30  per  cent  or  more).      The   min- 
eral coal  from  rocks  more  recent  than  the  Carboniferous 
formation   is   often   improperly   called  brown  coal,  even 
when  it   is   good   bituminous   coal,  without   a   brownish 
color  to  the  powder.     The  name  lignite  is  sometimes  also 
applied  to  it ;  but  true  lignite  is  coal  that  retains  the 
fibrous  texture  of  the  original  wood. 

3.  Mineral  Oil.  —  This  consists  of  liquid  hydrocarbons, 
and  is  chemically  related  to  illuminating  gas.  It  was 
formed  out  of  animal  or  vegetable  materials.  Illuminat- 
ing gas  is  often  given  off  in  great  quantities  from  the 
wells  or  sources  yielding  mineral  oil,  and  in  some  villages, 
in  oil  regions,  the  houses  are  heated  and  lighted  by  it. 
Many  black  shales  yield  mineral  oil  when  heated.  They 
do  not  contain  the  oil,  but  contain  other  hydrocarbons 


26  STRUCTURAL  GEOLOGY. 

(not  yet  satisfactorily  investigated)  which  yield  the  oil 
on  heating.  Mineral  oil,  on  long  exposure  to  the  air, 
combines  with  oxygen,  and  may  ultimately  become  a 
black  fusible  bitumen,  or  a  coal-like  substance  having 
little  or  no  fusibility. 

5.  CHLORIDES. 

The  only  chloride  forming  rock  masses  is  — 
Common  Salt,  or  Rock  Salt.  —  It  is  sodium  chloride 
(NaCl).  It  is  easily  distinguished  by  its  taste.  It 
constitutes  beds,  more  or  less  impure,  in  strata  of  various 
ages  from  the  Silurian  to  recent  time  ;  which  is  accounted 
for  by  the  fact  that  the  universal  ocean  is  an  abundant 
source  of  salt,  and  only  evaporation  is  required  to  deposit 
it.  Silurian  rock  salt  occurs  in  western  New  York,  and 
Upper  Canada ;  and  a  great  deposit,  probably  of  Creta- 
ceous age,  nearly  40  feet  thick  and  remarkably  pure, 
occurs  at  Petit  Anse,  Louisiana,  near  the  Gulf  of  Mexico. 
The  saline  constituents  of  the  ocean's  waters  constitute 
about  3.53  parts  in  100;  of  which  about  three  fourths  is 
common  salt,  the  rest  being  chiefly  magnesium  chloride, 
magnesium  sulphate,  calcium  sulphate,  or  gypsum,  potas- 
sium sulphate,  magnesium  bromide,  and  calcium  carbo- 
nate, with  traces  also  of  other  ingredients. 

6.  IRON   ORES. 

Iron  ores  are  widely  distributed  in  the  rocks,  and  some 
of  them  form  thick  beds.  Unlike  the  minerals  mentioned 
above,  they  have  a  specific  gravity  above  3.5.  The  most 
important  are  three  oxides,  three  sulphides,  and  a  car- 
bonate. 

The  sulphides,  however,  are  never  used  in  the  manu- 
facture of  iron,  since  no  process  is  known  by  which  iron 
can  be  economically  separated  from  sulphur. 

1.  Hematite,  or  ferric  oxide  (Fe2O3). — It  yields  a 
red  powder,  whence  its  name,  given  it  by  the  old  Greeks, 
from  aljjia,  blood.  Its  crystals  have  usually  an  iron-black 


CONSTITUTION   OF   ROCKS.  27 

color,  and  high  luster ;  but  it  is  deep  red  when  earthy  or 
impure.  It  is  the  source  of  the  color  in  red  sandstones 
and  some  other  red  rocks. 

2.  Limonite,  or  hydrous  ferric  oxide,  includes  two  equiv- 
alents of  Fe2O3  united  with  three  equivalents  of  water. 
It  varies  in  color  from  black  to  brown  and  yellow,  but 
yields  always  a  brownish  yellow  powder.    While  red  ocher 
of   painters  is   impure   hematite,  yellow  ocher  is  impure 
limonite.     Limonite  is  the  coloring  ingredient  in  a  large 
part  of  brown  and  brownish  yellow  rocks  and  clays.     The 
water  present  goes  off  on  heating,  and  hence  the  mineral, 
and  all  rocks  colored  by  it,  when  heated,  turn  red.     It 
is  formed  from  the  oxidation  and  hydration  of  various 
iron-bearing  minerals   (page   111),  and  often  makes  de- 
posits in  marshes  (page  116). 

3.  Magnetite.  —  Magnetite  has  an  iron -black  color,  like 
hematite ;  but,  unlike  that  ore,  it  is  attracted  strongly  by 
a  magnet,  and  yields  a  black  powder.     It  consists  of  three 
atoms  of  iron  and  four  of  oxygen  (Fe3O4).     It  is  common 
in  grains  in  many  rocks  (not  in  limestones),  and  among 
the  sands  of  seashores  and  soils ;  and,  like  hematite,  con- 
stitutes great  beds  among  the  older  rocks. 

Ferrous  oxide  (FeO)  never  occurs  as  a  mineral. 

4.  Pyrite  ;    Marcasite ;    Pyrrhotite.  —  Pyrite  is  an  iron 
sulphide   (FeS2),  of  a  brass-yellow  color,  and  nearly  as 
hard  as  quartz.      It  will  strike  fire  with  steel,  and  was 
named  by  the  Greeks  from  TTU/J,  fire.      It  is  common  in 
rocks,  in  massive  forms,  crystals  (often  cubes),  and  grains. 
Marcasite  has  the  same  composition  as  pyrite,  but  a  dif- 
ferent crystalline  form.     Pyrrhotite  is  the  name  of  another 
common  iron  sulphide,  containing  proportionally  less  sul- 
phur (FenS12),  having  the  color  of  bronze,  so  soft  as  to 
be  easily  scratched  with  the  point  of  a  knife,  and  somewhat 
strongly  attracted  by  a  magnet. 

5.  Siderite.  —  This  mineral,  called  also  iron  carbonate 
(FeCO3),  and  spathic  iron,  has,  when  crystallized,  approxi- 
mately the  cleavage  and  form  of  calcite.     The  color  is 


28  STRUCTUKAL   GEOLOGY. 

light  gray,  but  changes  readily  to  brown  on  exposure 
(by  alteration  of  more  or  less  of  the  material  to  limonite). 
It  is  much  heavier  than  calcite,  its  specific  gravity  being 
3.7  to  3.9.  It  effervesces,  like  dolomite,  in  heated  dilute 
hydrochloric  acid. 

The  ironstone,  or  clay  ironstone,  of  coal  regions,  used 
as  an  ore  of  iron,  is  generally  siderite  ;  that  of  other  than 
coal  regions  is  commonly  hematite  or  Ihnonite. 

Kinds  of  Rocks. 

PRELIMINARY  DEFINITIONS. 

Fragmental  and  Crystalline  Rocks.  —  The  minerals  of 
which  a  rock  consists  may  be  either  (1)  in  broken  or  worn 
grains  or  pebbles,  like  those  of  sand  or  mud  or  a  bed 
of  gravel ;  or  (2)  in  crystalline  grains,  in  which  case  they 
were  formed  where  they  now  are  at  the  time  of  the 
crystallization  of  the  rock.  Such  crystalline  grains  are 
angular,  as  may  be  seen  on  a  surface  of  fracture,  and,  in 
the  case  of  most  minerals  excepting  quartz,  show  surfaces 
of  cleavage.  Common  white  marble  and  granite  are  good 
examples  of  rocks  having  a  crystalline  texture ;  and, 
among  products  of  art,  such  a  texture  is  shown  in  loaf 
sugar  and  steel. 

The  rocks  of  the  first  kind,  consisting  of  fragments  of 
other  rocks,  are  called  fragmental  rocks  ;  and  those  of  the 
latter  kind,  crystalline  rocks.  Fragmental  rocks  are  also 
called  clastic  rocks,  from  the  Greek  /e\a£o>,  to  break. 

Besides  rocks  that  are  obviously  fragmental  and  those 
obviously  crystalline  there  are  others,  of  flinty  compact- 
ness, which  show  no  distinct  grains,  and  are  therefore  not 
easily  referred  to  either  division.  To  determine  the 
division  to  which  such  rocks  belong,  they  must  be  studied 
in  relation  to  the  rocks  associated  with  them.  If  these 
associated  rocks  are  fragmental,  then  the  compact  beds  are 
probably  so  also  ;  but,  if  these  are  crystalline,  then  the 
compact  beds  are  probably  crystalline.  The  examination 


CONSTITUTION   OF  BOCKS.  29 

of  thin  transparent  slices  with  the  microscope  is  often  the 
only  means  of  distinguishing  the  two  kinds.. 

Fragmental  Rocks.  —  These  are  the  most  common  of 
rocks,  constituting  by  far  the  largest  part  of  the  strata 
accessible  to  geological  study.  The  wear  and  decomposi- 
tion of  the  oldest  rocks  produced  fragmental  material  for 
those  of  the  next  period,  and  so  on  through  geological 
time  ;  and  the  rocks  made  of  such  material,  as,  for  ex- 
ample, sandstones,  shales,  and  conglomerates,  are  frag- 
mental rocks.  They  are  stratified  rocks  also,  because  they 
are  in  beds.  They  are  also  called  sedimentary  rocks, 
because  the  material  was  in  most  cases  deposited  as  a 
sediment  from  waters ;  and  detrital  rocks,  because  com- 
posed of  the  worn-out  material  (detritus)  of  older  rocks. 

While  the  great  majority  of  fragmental  rocks  were 
formed  as  sediments  from  water,  others  have  been  formed 
of  material  transported  by  glaciers  (see  page  162)  or  by 
wind  (see  page  120).  Still  other  fragmental  rocks  have 
resulted  from  the  accumulation  of  the  broken  rocks,  cin- 
ders, and  ashes  discharged  in  the  explosive  phase  of 
volcanic  eruptions. 

Crystalline  Rocks  are  either  igneous  or  metamorphic 
(with  the  exception  of  comparatively  small  accumulations 
in  veins  and  elsewhere,  formed  by  deposit  from  solution). 

Igneous  Rocks  include  those  which  have  come  up 
melted  through  volcanic  vents,  or  through  fissures  opened 
to  some  seat  of  melted  rock  within  the  earth's  crust. 
Besides  those  which  have  solidified  at  or  near  the  surface, 
other  igneous  rocks  have  solidified  at  considerable  depth 
below  the  surface.  Such  rocks  must  of  course  underlie 
all  superficial  rocks.  Igneous  rocks  solidified  at  great 
depth  may  subsequently  be  laid  bare  by  extensive  erosion. 
Igneous  rocks  include  lavas,  most  porphyry  and  granite, 
and  other  rocks  described  later  (pages  36-39). 

The  igneous  rocks  which  have  solidified  at  or  near 
the  surface  are  called  volcanic  rocks;  those  which  have 
solidified  at  great  depth,  plutonic  rocks.  In  their  more 


30  STRUCTURAL  GEOLOGY. 

typical  forms,  the  two  groups  are  strongly  distinguished 
from'  each  other,  though  indefinite  gradations  exist  be- 
tween them.  Plutonic  rocks  have  cooled  slowly  ;  and 
the  molecules  have  therefore  had  time  to  arrange  them- 
selves into  crystalline  grains  of  comparatively  large  size. 
Such  rocks  are  therefore  somewhat  coarsely  crystalline. 
Volcanic  rocks  have  cooled  rapidly,  and  the  process  of 
molecular  arrangement  was  therefore  interrupted  by 
solidification  before  large  crystals  could  be  formed.  Such 
rocks  are  therefore  fine-grained,  and  more  or  less  of  the 
material  (sometimes  nearly  the  whole)  is  amorphous  or 
glassy.  Plutonic  rocks  have  cooled  under  great  pres- 
sure. Thin  sections  examined  under  the  microscope  show 
innumerable  minute  cavities,  filled  most  commonly  with 
water,  more  rarely  with  carbon  dioxide  or  some  other 
material,  partly  in  liquid  condition,  but  with  a  bubble  of 
the  same  material  in  gaseous  form  floating  in  the  liquid. 
Volcanic  rocks  have  cooled  under  little  more  than  atmos- 
pheric pressure.  In  such  rocks  fluid  cavities  are  want- 
ing, since  volatile  materials  enveloped  in  the  mass  have 
been  able  to  escape. 

The  name  lava  is  applied  to  volcanic  rocks  in  general, 
especially  to  those  which  have  come  from  recent  volca- 
noes, and  to  those  which  show  a  vesicular  or  scoriaceous 
structure  (page  175). 

Metamorphic  Rocks  have  assumed  their  present  structure 
under  the  action  of  heat  and  other  subterranean  agencies 
without  fusion.  The  rocks  so  changed  were  probably  in 
most  cases  ordinary  fragmental  rocks  and  limestones.  The 
alteration,  when  most  perfect,  has  consisted  in  a  complete 
crystallization  of  the  rock,  and,  when  least  so,  in  its  con- 
solidation ;  between  which  extremes  all  gradations  exist. 
Examples  of  metamorphic  rocks  are  marble,  mica  schist, 
gneiss,  and  (probably)  some  granite. 

While  metamorphic  rocks  have  probably  been  derived 
for  the  most  part  from  the  alteration  of  sedimentary 
rocks,  it  appears  certain  that  in  some  cases  rocks  generally 


CONSTITUTION   OF   BOOKS.  31 

included  under  this  category  have  been  formed  tby  a  re- 
arrangement of  the  materials  of  igneous  rocks. 

Massive  Rocks.  —  Rocks  are  termed  massive  when  there 
is  no  tendency  to  part  along  parallel  planes,  so  as  to 
form  slabs  or  plates.  This  is  the  case  in  general  with  the 
coarser  fragmental  rocks,  as  sandstones  and  conglomer- 
ates, with  most  igneous  rocks,  and  with  many  limestones. 

Laminated,  Shaly,  Slaty,  Schistose  Rocks.  —  All  these 
terms  express  a  tendency  of  the  rock  to  part  along  parallel 
planes,  so  as  to  form  slabs  or  plates. 

In  laminated  and  shaly  rocks,  the  planes  of  division  are 
those  of  deposition  of  the  material.  These  structures 
belong,  accordingly,  to  sedimentary  rocks,  and  are  char- 
acteristic of  the  fine-grained  sediments.  The  shaly  struc- 
ture differs  from  the  laminated  in  that  the  plates  in  the 
former  are  thinner  and  more  fragile. 

In  slaty  rocks,  the  planes  of  division,  or  cleavage,  are 
independent  of  the  planes  of  deposition,  and  may  cross 
the  latter  at  any  angle.  The  slaty  structure  is  the  result 
of  pressure  subsequent  to  the  deposition  and  consolidation 
of  the  rock. 

In  schistose  (or  foliated)  rocks,  the  planes  of  division 
are  determined  by  the  parallel  arrangement  of  crystalline 
grains  of  some  cleavable  mineral,  as  mica,  hornblende, 
talc,  or  chlorite.  This  structure  is  characteristic  of  most 
of  the  metamorphic  rocks.  In  many  cases,  it  is  undoubt- 
edly the  result  of  the  original  stratified  arrangement  of 
the  material  in  a  sedimentary  rock.  But  in  other  cases 
such  a  parallel  arrangement  appears  to  be  due  to  pressure 
or  shearing,  causing  a  rearrangement  of  the  materials  of 
the  rock.  A  schistose  structure  may,  accordingly,  be 
developed  in  rocks  of  igneous  origin  or  in  vein  deposits. 

The  rocks  exhibiting  most  typically  the  laminated, 
shaly,  slaty,  and  schistose  structures  are  called  respec- 
tively flagstones  or  flags,  shales,  slates,  and  schists. 

Porphyritic  Rocks.  —  A  porphyritic  rock  is  one  hav- 
ing distinct  crystals  (usually  of  feldspar)  disseminated 


32  STRUCTURAL   GEOLOGY. 

through  a  fine-grained  or  compact  mass,  so  that,  when 
polished,  the  surface  shows  angular  spots  of  a  light-colored 
mineral,  usually  between  an  eighth  of  an  inch  and  two 
inches  in  length.  These  disseminated  crystals  are  called 
phenocrysts.  The  red  porphyry  of  Egypt,  and  the  green 
porphyry  of  the  eastern  borders  of  Greece,  much  used  for 
ornamental  purposes  by  the  ancients,  are  typical  examples. 
This  structure  is  very  frequent  in  felsite,  but  occurs  also  in 
granite  and  many  other  rocks.  It  is  especially  character- 
istic of  igneous  rocks.  The  phenocrysts  formed  slowly, 
while  the  remainder  of  the  material  was  still  fluid.  Later, 
under  other  conditions,  the  remainder  of  the  rock  solidified 
more  rapidly,  forming  the  fine-grained  or  compact  mass. 

Calcareous  Rocks.  —  Calcareous  rocks,  so  named  from 
the  Latin  calx,  lime,  are  the  limestones.  To  a  great  extent 
they  are  of  organic  origin  ;  that  is,  they  have  been  formed 
from  broken  or  pulverized  animal  relics,  such  as  shells  and 
corals  ;  and  in  this  case  they  are  properly  fragmental  beds, 
although  often  so  finely  compact  that  this  might  not  be 
suspected  from  their  texture. 

Some  limestones  have  been  made  from  the  accumula- 
tion and  consolidation  of  minute  shells,  called  Rhizopods. 
These  shells,  which  are  generally  no  larger  than  grains 
of  sand,  are  sometimes  entire,  but  generally  more  or  less 
broken.  Chalk  is  an  example  of  a  rock  made  of  Rhizopod 
shells. 

Limestones  made  from  fragments  of  earlier  limestones 
occur,  but  are  not  very  common.  Limestone  conglomer- 
ates are  of  this  kind. 

Other  calcareous  rocks  have  been  deposited  from  waters 
holding  the  material  in  solution,  and  are,  therefore,  of  chem- 
ical origin.  Of  this  kind  is  the  travertine  of  Tivoli  near 
Rome  in  Italy,  and  of  Gardiners  River  in  the  geyser 
region  of  the  Yellowstone  Park,  and  similar  beds  in  many 
regions  of  mineral  springs. 

Siliceous  Rocks.  —  Siliceous  rocks  are  those  that  con^ 
sist  largely  of  silica  in  the  form  of  quartz  or  (more  rarely) 


CONSTITUTION   OF   ROCKS.  33 

opal.  The  name  is  from  the  Latin  silex,  signifying  flint, 
a  variety  of  quartz.  Siliceous  material,  like  the  calca- 
reous, is,  as  stated  on  page  19,  of  both  mineral  and  organic 
origin  ;  but  the  mineral  is  vastly  the  more  abundant.  It 
sometimes  occurs  as  a  chemical  product,  as  in  the  siliceous 
depositions  about  geysers  (page  187).  The  silica  of 
chemical,  as  well  as  that  of  organic  origin,  is  often 
in  the  state  of  opal.  Opal,  by  solution  and  consolida- 
tion, may  become  converted  into  true  quartz,  as  in  flint, 
which  has,  for  the  most  part,  been  made  from  the  silica 
of  Sponges. 

The  principal  kinds  of  rocks  are  here  described  under 
the  three  heads  :  — 

1,  FRAG  MENTAL  ROCKS,  not  calcareous ;  2,  CRYSTAL- 
LINE ROCKS,  not  calcareous  ;  3,  CALCAREOUS  ROCKS. 


1.  FRAGMENT AL  ROCKS,  NOT  CALCAREOUS. 

The  fragmental  material  which  the  wear  and  decompo- 
sition of  rocks  ordinarily  produces  is  either  :  (1)  gravel 
or  shingle ;  (2)  sand  ;  (3)  mud,  earth,  or  clay. 

1.  Gravel.  —  The  pebbles  in  a  gravel  are  often  so  coarse 
as  to  be  readily  recognizable  as  fragments  of  various  rocks. 
Each  pebble  may  accordingly  contain  two  or  more  min- 
erals.    When  the  disintegration  of  rocks  proceeds  to  the 
point  of  pulverization,  each  grain  is  apt  to  consist  entirely 
of  a  single  mineral. 

2.  Sand.  —  Most  sand  consists  chiefly  of  quartz  ;   but 
in  some  sands  many  of  the  grains  are  of  feldspar  and  mica. 
Some  contain  much  clay,  or  are  argillaceous  (so  named 
from  argilla,  clay)  ;    some  are  red  or  brownish  yellow, 
owing  to  the  presence  of  iron  oxide,  and  are  called  ferru- 
ginous ;  some  will  effervesce  slightly  with  acid,  owing  to 
the  presence  of  some  calcareous  material.     Beach  sands 
often  contain  red  grains  of  garnet ;  and  commonly  black 
grains  of  magnetite,  which- a  magnet  easily  attracts. 


34  STRUCTURAL   GEOLOGY. 

3.  Mud,   Earth,    Clay.  —  Mud   and   earth  contain,  be- 
sides grains  of  quartz,  some  pulverized  feldspar,  or  else 
clay,  with  more  or  less  of  other  minerals.     The  terms 
argillaceous,  ferruginous,  calcareous,  are  here  applied  as 
above  ;    the  calcareous  grains  are  usually  derived  from 
the  grinding  up  of  shells.     When  black,  the  color  is  due 
to  carbonaceous  material  derived  from  vegetable  or  animal 
decomposition.      The  name  soil  is  applied  especially  to 
earth  containing  considerable  quantities  of  such  products 
of  organic  decomposition,  whence  its  fertility  is  largely 
derived. 

Common  clay  is  a  mixture  of  pure  clay  with  grains  of 
quartz,  feldspar,  and  usually  traces  of  hydrous  iron  oxide 
(limonite),  or  else  iron  carbonate.  Owing  to  the  iron,  it 
burns  red,  making  red  brick  —  heat  changing  the  iron 
mineral  present  to  hematite  (page  27).  Occasionally, 
as  in  certain  Milwaukee  clays,  the  iron  is  in  an  iron  sili- 
cate, so  that  the  heat  cannot  oxidize  it  ;  and  consequently 
the  bricks  it  makes  are  not  red.  Clays  free  from  iron  are 
required  for  white  pottery  ;  and  clays  free  from  grains  of 
feldspar,  for  making  fire-brick,  because  the  feldspar  is 
fusible. 

Pure  clay,  or  kaolin,  is  white,  and  feels  greasy.  It  is 
an  aluminium  silicate  containing  14  per  cent  of  water.  It 
results  from  the  decomposition  of  feldspar  (pages  113, 116). 
It  is  used  in  making  fine  pottery  and  porcelain,  and  also 
in  giving  body  to  paper. 

Rock  flour  is  finely  pulverized  rock  of  any  kind. 

The  consolidation  of  gravel,  sand,  and  mud  or  clay,  pro- 
duces, respectively,  conglomerate,  sandstone,  and  shale. 

4.  Conglomerate.  —  Consolidated  gravel.     If  the  stones 
are  rounded,  the  rock  is  often  called  a  pudding-stone  ;  if 
in  the  form  of  angular  fragments,  a  breccia ;  if  the  peb- 
bles are  of  quartz,  a  siliceous  conglomerate,  or,  when  very 
firmly  consolidated,  a  grit ;    if  of  limestone,  a  calcareous 
conglomerate.     The   stones  may  be    a   foot   or   more  in 
diameter,  though  usually  much  smaller. 


CONSTITUTION    OF    ROCKS.  35 

5.  Sandstone.  —  A  rock  made  of  sand.     Common  colors 
are  red,  gray,  brown,  white.     If  composed  of  quartz  sand, 
it    is   a  quartzose  or  siliceous  sandstone  ;    if   of  granite 
sand,  a  granitic  sandstone ;   if  fine,  earthy  or  clayey,  an 
argillaceous  sandstone ;  if  containing  some  calcium  car- 
bonate, a  calcareous  sandstone.     It  makes  a  durable  build- 
ing stone  when  firm,  if  not  much  absorbent  of  water  when 
immersed  in  it,  and  if  free  from  pyrite  so  as  not  to  rust 
on  exposure.     The  brownish  red  sandstone  is  often  called 
freestone.     The  sandstone  used  for  grindstones  is  even- 
grained  and  more  or  less  friable. 

6.  Shale. — A  rock  resulting  from  the  consolidation  of 
clay  or  clayey  earth  or  fine  mud,  and  splitting  readily  into 
rather  thin  laminae  parallel  to  the  planes  of  stratification 
(page  31).     The  colors  are  of  all  dull  shades  from  gray 
to  red  and  black.     Carbonaceous  shale  is  a  blackish  kind, 
yielding  mineral  oil.     Alum  shale  is  a  shale  which  has 
become  impregnated  with  alum  through  the  decomposition 
of  the  pyrite  it  contains. 

7.  Tufa.  —  A  volcanic  sandstone,  composed  of  volcanic 
sand  or  ashes  (see  page  175).    The  color  is  usually  brown- 
ish, grayish,  or  reddish. 

2.  CRYSTALLINE  ROCKS,  NOT  CALCAREOUS. 

The  most  important  of  these  rocks  may  be  arranged 
conveniently  in  four  groups  according  to  their  miner- 
alogical  composition. 

1.    KOCKS    CONSISTING    CHIEFLY    OF    QuARTZ    (OB   OPAL). 

1.  Quartzite. — A  metamorphosed  quartzose  sandstone. 
It  is  usually  a  very  hard  rock.  It  may  be  distinguished 
from  the  accumulations  of  quartz  in  veins  by  its  granular 
structure  (as  seen  under  a  lens,  or  in  thin  sections  under 
the  microscope).  Itacolumite,  or  flexible  sandstone,  is  a 
laminated,  porous  quartzite  containing  minute  scales  of  a 
hydrous  mica,  which  render  the  rock  somewhat  flexible. 


36  STRUCTURAL  GEOLOGY. 

2.  Chert.  —  An  impure  flint  or  hornstone  occurring  in 
beds  or  nodules  in  some  stratified  rocks. 

3.  Siliceous  Sinter.  —  Deposits  of  silica  from  solution 
in  water,  most  commonly  formed  by  hot  springs.     The 
silica   is   usually  opal,  more  rarely   quartz.     The   sinter 
deposited  by  geysers  (page   187)  is  often  called  gey- 
serite. 

2.  ROCKS  CONSISTING  OF  POTASH  FELDSPAR,  WITH  OR  WITH- 
OUT QUARTZ,  AND  USUALLY  WITH  MICA  OR  HORNBLENDE. 

1.  Granite.  —  A  rock  consisting  of  quartz,  feldspar,  and 
mica,  generally  so  coarsely  crystalline  that  its  ingredients 
are  conspicuous  to  the  naked  eye.     Color,  usually  light  or 
dark  gray,  or  flesh-red,  the  latter  shade  derived  from  a 
flesh-colored  feldspar;  the  quartz,  uncleavable  and  usually 
light  grayish  or  smoky  in  color;  the  feldspar,  white  to 
flesh-red,  and  yielding  smooth,  shining  surfaces  by  cleav- 
age ;  the  mica,  white  to  black,  and  affording  thin,  flexible 
leaves  by  cleavage.     Most  granite  is  igneous,  and  exhibits 
most  typically  the  characters  of  the  plutonic  rocks.    Some 
granite  appears  to  be  metarnorphic.    Some  granite  appears 
to  constitute  true  veins  (page  198). 

2.  Gneiss.  —  Like  granite  in  constitution,  but  having  a 
schistose  structure,  owing  to  the  arrangement  of  the  min- 
erals, the  mica,  especially,  being  in  parallel  planes  ;  it  has, 
therefore,  a  banded  appearance  on  a  surface  of  transverse 
fracture.     If  the  color  of  the  gneiss  is  dark  gray,  it  is 
banded  usually  with  black  lines  consisting  largely  of  black 
mica.     Along  the  micaceous  planes  it  breaks  rather  easily 
into  slabs,  which  are  sometimes  used  for  flagging.    Gneiss, 
has  probably  been  formed  in  most  cases  by  the  metamor- 
phism  of  argillaceous  sandstones.    But  other  gneisses  have 
been  formed  from   granites  by  pressure  or  shearing,  by 
which  the  ingredients  have  been  forced  into  a  parallel 
arrangement. 

3.  Mica  Schist.  —  Related  to  gneiss,  but  consisting  more 
largely  of  mica,  with  usually  less  quartz  and  very  much 


CONSTITUTION  OF  HOCKS.  §7 

less  feldspar,  and,  in  consequence  of  the  mica,  breaking 
into  thin  slabs.  The  slabs  have  a  glistening  surface.  In 
regions  of  mica  schist  the  dust  of  the  roads  is  often  full  of 
shining  particles  of  mica.  Mica  schist  is  generally  a  meta- 
morphic  rock,  and  the  same  is  probably  true  of  most  of  the 
schists. 

4.  Hydromica  Schist.  —  A  slaty,  fine-grained  mica  schist, 
feeling  somewhat  greasy  to  the  fingers.     It  used  to  be 
called  talcose  slate ;  but  it  contains  a  hydrous  mica  instead 
of  talc. 

5.  Slate,  Argillite,  Phyllite. — The  rocks  included  under 
these  names  form  a  transition  between  the  shales  and  the 
hydromica  schists,  and  may  with  about  equal  propriety  be 
placed  in  either  position  in  the  classification,  being  the 
result  of  a  very  feeble  metamorphism.     The  texture  ap- 
pears to  the  naked  eye  hardly  crystalline.     They  are  fine- 
grained rocks ;  and  the  kinds  valued  as  roofing  slates  and 
drawing  slates  are  hard,  smooth,  and  not  absorbent  of 
water.     The    color   is   usually   dark   gray,   passing    into 
bluish,  greenish,  and  reddish  shades.     In  these  rocks  the 
slaty  structure  is  most  perfectly  displayed.     As  already 
explained  (page  31),  the  planes  of  slaty  cleavage  are  inde- 
pendent of  the  planes  of  stratification,  and  are  due  to 
pressure  (page  219). 

Perfectly  gradual  transitions  may  be  traced  from  granite 
to  gneiss,  from  gneiss  to  mica  schist,  from  mica  schist  to 
hydromica  schist,  from  hydromica  schist  to  slate,  and  from 
slate  to  shale. 

6.  Hornblende  Granite,  Quartz  Syenite.  —  A  rock  resem- 
bling granite,  but  containing  hornblende  instead  of  mica. 
Intermediate  kinds  occur,  in  which  both  mica  and  horn- 
blende are  present.     Generally  plutonic,  like  true  granite. 

7.  Syenite.  —  Like  the  preceding,  but  with  little  or  no 
quartz.      Plutonic. 

8.  Syenite    Gneiss,    Hornblende    Gneiss.  —  Related    to 
hornblende    granite    precisely   as    gneiss    is    related    to 
granite. 


38  STRUCTURAL  GEOLOGY. 

9.  Hornblende   Schist. — Related   to   the   preceding   as 
mica  schist  is  related  to  gneiss,  the  micaceous  and  horn- 
blendic  series  showing  a  close  parallelism.     Generally  a 
metamorphic  rock.     Sometimes  formed   by  alteration  of 
diorite  or  some  such  igneous  rock. 

10.  Felsite.  —  A  fine-grained,  often  porphyritic  rock, 
consisting    chiefly    of    orthoclase,    containing    no    glass. 
When  quartz  is  present   in   considerable  quantity,  it  is 
called  quartz  felsite.     Much   of   the   so-called   porphyry 
belongs  here.     The  colors  are  various,  grayish  and  red- 
dish shades  being  common.     An  igneous  rock. 

11.  Rhyolite.  —  Similar  in  composition  to  a  quartz  fel- 
site, but  showing  under  the  microscope  the  presence  of 
glass,  indicating  rapid  cooling.     It  is  one  of  the  common 
kinds  of  lava. 

12.  Trachyte.  —  Consists,  like  felsite,  chiefly  of  ortho- 
clase, but  differs  from  felsite  in  containing  some  glass. 
The  feldspar  is  partly  of  a  variety  occurring  in  crystals  of 
glassy  luster,  called  sanidin.     One  of  the  most  common 
lavas. 

13.  Obsidian.  —  A  lava  having  substantially  the  chemi- 
cal composition  of  a  rhyolite  or  trachyte,  but  cooled  so 
rapidly  as  to  be  almost  entirely  glassy. 

3.  BOCKS   CONSISTING  OF   A   SODA-LIME   FELDSPAR,    WITH 
HORNBLENDE  OR  PYROXENE. 

1.  Diorite.  —  Differs  from  syenite  in  containing  a  soda- 
lime  feldspar  (generally  oligoclase)  instead  of  orthoclase. 
Coarsely  or  finely  crystalline,  containing  no  glass.     It  is 
sometimes  porphyritic,  and  the  classical  red  porphyry  of 
Egypt  (rosso  antico)  is  here  included.     Rather  dark  gray- 
ish and  greenish  colors  predominate.     It  is  generally  an 
igneous  rock,  though  it  may  be  sometimes  metamorphic. 

2.  Andesite.  —  Similar   in  composition   to   diorite,  but 
partly  glassy.     A  common  kind  of  lava. 

3.  Gabbro.  —  A    coarsely   crystalline    rock,    consisting 
chiefly  of*  a  soda-lime' feldspar  (generally  labradorite)  and 


CONSTITUTION   OF   KOCKS.  39 

pyroxene,  often  containing  magnetite  and  chrysolite  as 
accessory  ingredients.  In  its  coarseness  of  crystallization 
it  resembles  granite ;  and,  like  granite,  is  generally  a 
plutonic  rock. 

4.  Dolerite,  Diabase.  —  Similar  in  composition  to  gab- 
bro,  but  not  so  coarsely  crystalline.     Often  porphyritic. 
Colors  dark — black,  shading  into  gray,  greenish,  or  brown- 
ish  colors.     An   igneous   rock,  very  often    occurring   in 
dikes.     This   and   other  dark   heavy  igneous   rocks   are 
often  called  trap. 

5.  Basalt.  —  Similar  in  composition  to  gabbro  and  dole- 
rite,  but  showing  the  typical  volcanic  character  of  contain- 
ing glass.     The  rock  (or  the  ground  mass,  when  the  rock 
is  porphyritic)  is  so  fine-grained  as  to  appear  compact  to 
the  naked  eye.     Color  black,  or  nearly  so.     One  of  the 
most  common  kinds  of  lava. 

6.  Tachylite.  —  A  lava  substantially  similar  to  basalt  in 
chemical  composition,  but  cooled  so  rapidly  as  to  be  almost 
entirely  glassy. 

4.  BOCKS  CONSISTING  CHIEFLY  OF  HYDROUS  MAGNESIAN 
SILICATES. 

1.  Chlorite   Schist.  —  A  schistose  rock  of  dark  green 
color,  consisting  chiefly  of  chlorite.     It  is  connected  by 
intermediate  gradations  with  hydromica  schist. 

2.  Talc  Schist.  —  A  schistose  rock  of  grayish  or  green- 
ish color  and  greasy  feel,  consisting  chiefly  of  talc.     A 
comparatively  rare  rock,  most  of  the  rocks  to  which  the 
name  has  been  applied  being  hydromica  schist. 

3.  Steatite,  Soapstone.  —  Like  talc  schist,  except  in  the 
lack  of  the  schistose  structure.     The  finer-grained  varieties 
are  used  for  slate  pencils  and  for  various  other  purposes. 

4.  Serpentine.  —  A  rock  consisting  chiefly  of  the  min- 
eral serpentine.     In  most  cases  it  results  from  the  hydra- 
tion  of  rocks  consisting  wholly  or  largely  of  anhydrous 
magnesian    silicates.     Rocks    containing    chrysolite    are 
especially  liable  to  undergo  this  alteration. 


40  STRUCTURAL  GEOLOGY. 

3.    CALCAREOUS  ROCKS. 
1.    NON-METAMORPHIC. 

1.  Common  Limestone.  —  A  compact  rock  of  grayish  and 
other  dull  shades  of  color  to  black,  consisting  either  of 
calcite  or  dolomite,  but  often  impure  from  the  presence  of 
clayey  or  earthy  material.     It  breaks  with  little  or  no 
luster.     If  containing  fossils,  it  is  called  fossiliferous  lime- 
stone ;  if  the  fossils  are  Corals,  coral  limestone  ;  if  remains 
of  Crinoids,  crinoidal  limestone.     When  impure,  and  there- 
fore good  for  making  hydraulic  lime  (quicklime  that  will 
make  a  cement  which  sets  under  water),  it  is  called  hydrau- 
lic limestone.     Chalk  is  a  variety  of  limestone  soft  enough 
to  be  used  for  marking,  and  consisting  chiefly  of  shells  of 
Rhizopods. 

Many  varieties  of  common  limestone  are  polished  and 
used  as  marbles ;  they  have  black,  reddish,  yellow,  gray, 
and  other  colors  ;  kinds  containing  fossil  shells  are  called 
shell  marbles. 

2.  Oolite.  —  A  limestone  consisting   of   concretions  as 
small  as  the  eggs  in  the  roe  of  fish,  or  smaller — whence  the 
name,  from  the  Greek  o>oV,  egg.     Oolitic  limestone  occurs 
in  all  the  geological  formations,  and  is  forming  in  modern 
seas  about  the  Florida  Keys  and  in  other  coral-reef  regions. 

3.  Stalactite,  Stalagmite,  Travertine.  — Stalactites  are  ac- 
cumulations of  limestone  hanging  from  the  roofs  of  caverns; 
and  stalagmite  is  the  same  material  covering  the  floors;  both 
are  formed  from  the  calcareous  waters  that  come  through 
the  roof,  and  are  sometimes  called  dripstone.     A  similar 
deposit  from  streams  or  ponds  is  called  travertine  ;  it  is 
sometimes  used  for  a  building  stone. 

4.  Marl.  —  Clay  containing  much  calcium  carbonate,  and 
hence  used  as  a  fertilizer.     The  term  is  used  popularly  for 
any  rock  material  that  can  be  so  used.     Shell  marl  consists 
largely  of  shells.     Greensand  marl  is  sand  consisting  largely 
of  grains  of  a  green   silicate  of   iron  and  potash  called 
glauconite. 


ROCK  MASSES,  OR  TERRANES.  41 

2.   METAMORPHIC. 

Crystalline  Limestone;  Architectural  and  Statuary  Mar- 
ble.—  Limestone  having  a  crystalline  texture,  and,  conse- 
quently, glistening  on  a  surface  of  fracture.  A  pure,  white 
kind,  of  fine  grain,  is  used  for  statuary,  and  both  this 
and  coarser  varieties  for  marble  buildings.  Many  of  the 
clouded  marbles  are  here  included. 

II.    ROCK   MASSES,   OR   TERRANES. 

The  rocks  above  described  are  the  material  of  which  the 
great  rock  masses,  or  terranes,  of  the  globe  consist.  These 
rock  masses  are  either  stratified  or  unstratified. 

The  Stratified  Condition.  —  Stratified  rocks  are  those 
which  lie  in  beds  or  strata.  The  word  stratum  (the 
singular  of  strata)  is  from  the  Latin,  and  signifies  that 
which  is  spread  out. 

In  geology,  a  stratum  includes  all  the  beds  of  one  kind 
of  rock  (as  of  limestone,  or  of  sandstone,  or  of  any  other 
kind)  that  lie  in  one  continuous  series. 

The  earth's  rocky  strata  are  spread  out  in  beds  of  vast 
extent,  many  of  them  thousands  of  square  miles  in  area 
and  thousands  of  feet  in  thickness. 

The  stratified  rocks  exposed  to  view  over  the  earth  far 
exceed  in  area  the  unstratified.  They  are  the  rocks  of 
nearly  the  whole  of  the  United  States  and  of  almost  all 
of  North  America,  and  not  less  of  the  other  continents. 
Throughout  central  and  western  New  York,  and  the  states 
south  and  west,  the  rocks,  wherever  exposed,  are  seen  to 
be  made  up  of  a  series  of  beds.  And,  if  the  rocks  are  less 
distinctly  stratified  over  most  of  New  England,  it  is,  in 
general,  only  because  the  structure  has  been  partly  obscured 
by  the  upturning  and  crystallization  they  have  undergone 
since  they  were  formed. 

Fig.  13  represents  a  section  of  the  rocks  along  the 
river  below  Niagara  Falls.  It  gives  some  idea  of  the 


42  STRUCTURAL   GEOLOGY. 

alternations  which  occur  in  the  strata.  In  a  total  height 
of  250  feet  (165  feet  at  the  falls,  at  F,  on  the  right) 
there  are,  on  the  left,  six  different  strata  in  view,  and 
parts  of  two  others,  the  upper  and  lower,  making  eight  in 
all.  Number  1  is  shale  ;  2,  sandstone  ;  3,  shale  ;  4,  sand- 
stone ;  5,  shale ;  6,  limestone ;  7,  shale ;  8,  limestone. 
Only  two  of  these  strata,  7  and  8,  are  in  sight  at  the  Falls 
(at  F).  The  alternations  are  thus  numerous  and  various  in 
most  regions  of  stratified  rocks.  Along  the  canon  of  the 
Colorado,  there  are  in  some  places  more  than  8000  feet  of 
consecutive  stratified  beds,  showing  their  edges  in  lofty 
precipices,  and  in  the  mountains  towering  above  the  adjoin- 
ing plains.  Fig.  14  represents  one  of  the  scenes  along 
the  canon. 

FIG.  13. 


w  F 

Section  along  the  Niagara  River. 

It  must  not  be  inferred  that  the  earth  is  covered  by  a 
regular  series  of  coats,  the  same  in  all  countries  ;  for  this 
is  far  from  the  truth.  Many  strata  occur  in  New  York 
that  are  not  found  in  Ohio  and  the  states  west,  and  many 
in  southern  New  York  that  are  not  found  in  the  northern 
part.  Moreover,  a  stratum  of  limestone  may  change  in 
the  course  of  a  few  miles  to  one  of  sandstone  or  shale. 

A  layer  is  one  of  the  subdivisions  of  a  stratum.  A 
stratum  may  consist  of  an  indefinite  number  of  layers. 

In  many  stratified  rocks,  as  in  most  limestones,  con- 
glomerates, and  the  coarser  sandstones,  the  strata  or 
layers  are  thick,  and  the  structure  of  the  rock  is  massive 
(page  31).  But  argillaceous  sandstones  and  shales  gen- 
erally split  into  thin  layers,  showing  thus  a  laminated  or 
shaly  structure.  Sometimes  the  rock  shows  on  cross  frac- 


BOOK  MASSES,   OR   TERRANES. 


43 


ture  a  minutely  banded  appearance,  due  to  variation  in 
the  color  or  texture  of  the  deposit,  even  though  the  thin 
layers  may  not  be  separable.  Such  minutely  banded 
rocks  are  said  to  be  straticulate,  whether  the  layers  are 
separable  or  not. 


Fio.  14. 


Wall  of  Colorado  Cafton. 

A  system  includes  all  the  various  kinds  of  strata  that 
were  formed  in  one  age  or  era,  as  the  Carboniferous  sys- 
tem, or  that  of  the  Coal.  The  term  series  is  used  like 
system,  but  with  most  writers  it  denotes  a  less  extensive 
division.  Subdivisions  of  a  system  or  series  are  called 
groups  ;  a  subdivision  of  a  group,  a  stage.1 

1  There  is  no  uniformity  of  usage  among  geologists,  in  regard  to  the 
order  of  the  terms  defined  in  this  paragraph. 


44  STRUCTURAL   GEOLOGY. 

The  term  formation  is  often  used  instead  of  system  or 
series.  But  it  is  also  employed  to  designate  all  the  rocks 
of  a  kind  making  a  continuous  mass  in  a  region,  as  a 
limestone  formation,  a  coral  formation,  a  granite  formation. 

Origin  of  Stratification.  —  The  stratified  structure  is 
due  to  changes,  at  longer  or  shorter  intervals,  in  the 
formations  in  progress  over  a  region.  For  a  long  time 
limestones  may  have  been  forming.  Then,  through  some 
change  in  the  conditions  —  it  may  be  a  change  of  level,  or 
of  marine  currents,  —  sandstones  were  formed  over  the 
limestone  stratum.  After  another  change,  deposits  of 
mud,  or  clay,  or  pebbles,  succeeded.  Such  alternations 
have  been  going  on  in  one  part  or  another  of  the  seas  over 
the  continental  areas,  through  all  geological  time. 

Changes,  also,  in  kinds  of  species  populating  the  seas 
have  helped  to  mark  the  distinction  in  successive  strata; 
though  generally  in  connection  with  some  physical  or 
geographical  change,  as  change  of  currents,  or  of  tem- 
perature in  the  waters,  or  of  their  purity,  or  of  level, 
increasing  or  diminishing  the  depth.  According  as  such 
changes  occur  at  long  or  short  intervals,  the  beds  conse- 
quently produced  are  of  greater  or  less  thickness. 

In  all  cases,  the  subdivisions  are  due  to  changes  of 
conditions ;  and,  for  the  very  thin  layers  of  the  straticu- 
late  structure,  those  changes  may  be  the  daily  alterna- 
tions or  ebb  and  flow  of  the  tides ;  or  the  changes  of 
velocity  in  the  blasts  of  wind  over  a  region  of  sand ;  or 
the  successive  throws  of  the  breakers  over  a  beach ;  or 
simply  wavelike  vibrations  in  any  body  of  water.  For  a 
wave  has  its  time  of  maximum  and  minimum  movement, 
and  therefore  its  times  of  unequal  force  in  the  process  of 
deposition,  and  waters  of  breakers  descending  a  beach 
have  their  time  of  action  succeeded  by  a  time  of  rest. 

In  volcanic  work,  also,  there  are  alternations.  Out- 
flows of  lava  are  separated  from  one  another  by  intervals 
of  rest,  or  by  times  when  only  steam,  other  gases,  and 
volcanic  ashes  are  ejected. 


ROCK  MASSES,    OR   TERRANES.  45 

Thus  strata,  beds,  layers,  from  the  coarsest  stratification 
to  the  finest  straticulation,  have  one  general  cause ;  and 
bedding  is  absent  from  deposits  only  when  alternations 
did  not  occur  during  the  deposition,  or  when  the  mate- 
rials, as  those  of  many  conglomerates,  are  too  coarse  to 
admit  of  the  finer  bedding. 

Unstratified  Condition.  —  Unstratified  rocks  are  those 
which  do  not  lie  in  beds  or  strata.  Mountain  masses  of 
granite  are  usually  without  any  appearance  of  stratifica- 
tion. The  rock  of  the  Palisades,  on  the  Hudson,  stands 
up  with  a  bold  columnar  front,  and  has  no  division  into 
layers.  Most  volcanic  formations  exhibit  a  sort  of  strati- 
fication, due  to  the  alternations  mentioned  above ;  though 
the  name  stratification  is  not  usually  applied  technically 
to  volcanic  rocks.  But  in  some  volcanic  regions  the  rocks 
rise  into  lofty  summits  without  stratification.  Veins 
(page  196),  dikes  (page  188),  and  other  special  modes  of 
occurrence  of  Unstratified  rock  will  be  described  hereafter. 

Relation  of  Stratified  and  Unstratified  Rocks  in  the 
Earth's  Crust.  —  The  relations  of  the  stratified  and  un- 
stratified  rocks  in  the  earth's  crust  will  be  understood 
after  considering  the  origin  of  the  crust. 

The  Unstratified  rocks  which  once  formed  the  surface  of 
the  globe  were  made  by  the  solidification  of  the  molten  mass. 

After  the  solidifying  of  the  sphere  at  surface,  the  ocean 
commenced  at  once  to  make  fragmented  stratified  rocks 
over  the  exterior  through  the  wear  of  those  primitive 
Unstratified  rocks,  and  the  stratifying  of  the  sand  or  mud 
thus  made.  The  ocean  thus  worked  over  and  covered  up 
with  strata  nearly  all,  if  not  all,  the  original  Unstratified 
crystalline  rocks.  Hence  the  areas  of  the  Unstratified 
rocks  that  were  made  in  the  first  solidification  of  the 
globe,  are  of  very  small  extent  over  the  continents,  if 
visible  anywhere. 

Geology  has,  for  its  study,  chiefly  stratified  rocks. 
Much  the  larger  part  of  all  the  facts  in  geological  history 
are  derived  from  rocks  of  this  kind,  and  therefore  the 


46 


STRUCTURAL   GEOLOGY. 


FIG.  15. 


various  details  with  regard  to  their  structure  and  arrange- 
ment are  of  the  highest  importance. 

Concretions.  —  Rocks  often  contain,  and  sometimes  con- 
sist of,  small  spheres  or  disks  of  mineral 
matter,  which  are  called  concretions.  Con- 
cretions result  from  a  tendency  in  matter  to 
concrete  or  solidify  around  centers.  Some  are 
no  larger  than  grains  of  sand,  or  the  eggs  in 
the  roe  of  fish,  as  in  oolitic  limestone  (page 
40).  Others  are  as  large  as  peas  or  bullets, 
and  others  a  foot  or  more  in  diameter. 
Fig.  15  represents  a  spherical  concretion  ;  Fig.  16,  a 
rock  made  up  of  rounded  concretions,  having  a  concentric 


A  spherical  concre- 
tion. 


FIG.  16. 


FIG.  IT. 


Concretions  with  concentric  structure. 


Disk-shaped  concretions. 


FIG.  18. 


structure;   frig.    17,   one   with   flattened   or   disk-shaped 
concretions. 

Concretions  are  made  by  the  deposit  of  calcium  car- 
bonate or  some  other  material  held  in 
solution  or  suspension  by  waters  per- 
colating through  the  rock.  They  are 
usually  spherical  in  massive  sandstones, 
because  solutions  in  such  rocks  spread 
equally  in  all  directions ;  but  lenticular 
in  laminated  rocks,  and  flattened  disks 
in  argillaceous  rocks  or  shales,  because 
in  these  rocks  waters  spread  laterally 
more  easily  than  vertically.  All  these  kinds  are  shown 
in  Fig.  18, 


Strata  containing  con- 
cretions. 


BOCK  MASSES,   OR  TERKANES. 


47 


The  balls  are  sometimes  hollow,  and  the  disks  mere 
rings.  Frequently  the  concretions  have  a  shell  or  other 
organic  object  at  center  (Fig.  19).  They  are  often  cracked 
through  the  interior  (Fig.  20)  from  drying  (some  soft 
clayey  muds  contracting  to  a  tenth  of  their  bulk)  ;  the 
outside  in  such  a  case  solidified  while  the  inside  was  still 


FIG.  19. 


FIG.  20. 


FIG.  21. 


Concretion  with  a  fossil 
at  its  center. 


Concretion  with 
shrinkage  cracks. 


Geode. 


moist.  The  cracks  may  afterward  become  filled  with  other 
minerals.  Sometimes  they  contain  a  loose  ball  within — 
a  concretion  within  a  concretion.  A  cavity  lined  with 
crystals  (Fig.  21)  is  called  a  geode ;  but  the  hollow  balls 
so  lined  within  are  not  generally  concretions. 

Joints.  —  The  rocks  of  a  region  are  often  divided  very 
regularly  by  numerous  planes  of  fracture,  the  most  of  them 


FIG.  22. 


Jointed  structure,  shore  of  Cayuga  Lake. 

parallel  to  one  another,  and  cutting  through  the  strata, 
perpendicularly,  or  at  various  angles,  to  great  depths, 
but  with  the  walls  of  the  fissures  generally  in  contact  or 
but  slightly  separated.  Such  deep  unopened  fractures 
may  characterize  the  rocks  over  areas  hundreds  of  miles 
in  extent.  They  are  called  joints  ;  and  a  rock  thus  divided 
is  said  to  present  a  jointed  structure.  In  many  cases  .there 


48 


STRUCTURAL  GEOLOGY. 


are  two  systems  of  joints  or  divisional  planes  in  the  same 
region,  crossing  one  another ;  and  the  undermining  of  a 
bluff  of  jointed  beds  and  tumbling  down  of  masses  lead 
to  the  production  of  forms  like  those  of  fortifications  or 
broken  walls,  as  shown  in  Fig.  22,  representing  a  view 
on  the  shores  of  Cayuga  Lake.  The  directions  of  such 
joints  are  facts  which  the  geologist  notes  down  with  care. 
Slaty  Cleavage.  —  The  peculiar  structure  of  slates  and 
allied  rocks  (cleavage)  has  been  referred  to  on  page  81 ; 
and  it  has  been  -stated  that  the  planes  of  cleavage  are 
usually  not  parallel  to  the  bedding  ;  that  is,  they  cross  the 
layers  of  stratification  more  or  less  obliquely,  instead  of 
conforming  to  the  layers  of  bedding  like  the  divisional 
planes  in  the  shaly  structure.  Slaty  cleavage  is  in  this 
respect  like  the  jointed  structure  ;  but  it  has  the  divisional 
planes  so  numerous  that  the  rock  divides  into  slates  in- 


FIG.  28. 


Fir,.  24. 


Slaty  cleavage. 

stead  of  blocks ;  and  the  two  differ  in  mode  of  origin. 
Slaty  cleavage  is  confined  to  fine-grained  rocks.  In  Fig. 
23,  the  lines  of  bedding  or  stratification  are  shown  at  a,  5, 
<?,  d,  while  the  transverse  lines  correspond  to  the  direction 
of  the  cleavage.  The  same  is  shown  in  Fig.  24,  with  the 
addition  of  a  slight  irregularity  in  the  slates  along  the 
junction  of  two  layers. 

POSITIONS  OP  STRATA. 

1.  Original  Position  of  Strata.  — Horizontal  Position.  — 
Ordinary  stratified  rocks  were  once  beds  of  sand  or  earth, 
or  of  other  rock  material,  spread  out  by  the  currents  and 
waves  of  the  ocean,  or  the  waters  of  lakes  or  rivers,  or 
by  the  winds. 


ROCK   MASSES,   OR   TERRANES.  49 

When  the  larger  portion  of  the  beds  over  the  North 
American  continent  were  formed,  the  continent  lay  to  a 
great  extent  beneath  the  ocean,  as  the  bottom  of  a  great, 
though  mostly  shallow,  continental  sea.  The  principal 
mountain  chains  —  the  Rocky  Mountains  and  the  Appa- 
lachians—  had  not  been  made,  and  the  surface  of  the 
submerged  land  was  nearly  flat.  That  those  beds  were 
really  marine,  is  proved  by  their  containing,  in  most  cases, 
marine  shells,  crinoids,  or  corals,  the  relics  of  marine  life ; 
and  that  the  continental  seas  had  great  extent,  is  proved 
by  the  fact  that  the  beds  cover  surfaces  tens  of  thousands 
of  square  miles  in  area,  some  of  them  reaching  from  the 
Atlantic  border  westward  beyond  the  Mississippi.  In 
those  large  continental  seas,  the  deposits  made  by  means 
of  the  currents  and  waves  were  nearly  or  quite  horizontal. 
Wherever  they  reached  the  surface,  like  the  sand  flats  off 
many  modern  seashores,  the  sweep  of  the  waters  over 
them  during  the  incoming  tide  would  tend  to  plane  off  and 
keep  level  the  upper  surface  of  the  beds,  whether  accumu- 
lations of  sand  or  earth,  or  of  shells  or  corals.  If  the  bottom 
over  the  region  were  very  slowly  sinking,  the  accumulations 
might  go  on  thickening,  and  the  beds  continue  to  have 
the  same  level  or  horizontal  position.  Strata  formed  along 
the  borders  of  rivers  and  lakes  are  nearly  horizontal,  and 
so  are  those  on  the  borders  of  the  ocean ;  and  for  a  like 
reason,  that  the  water  works  with  reference  to  its  surface, 
which  is  horizontal.  Moreover,  the  bottom  of  the  border 
of  the  Atlantic,  south  of  Long  Island,  for  80  miles  from 
the  coast  line  (see  Fig.  3,  page  13),  deepens  only  1  foot  for 
every  600  to  700  ;  and,  if  the  area  were  above  the  ocean, 
no  eye  would  detect  that  it  was  not  a  perfect  level. 

The  view  of  the  rocky  wall  of  the  Colorado  Canon,  on 
page  43,  illustrates  well  the  approximate  horizontally  of 
the  original  bedding,  and  shows  that  it  was  continued 
through  many  long  periods  ;  for  the  series  of  rocks,  more 
than  5000  feet  thick,  represents  a  long  succession  of  geo- 
logical formations. 


50 


STRUCTURAL  GEOLOGY. 


Some  beds  were  originally  vast  marshes,  like  the  marshes 
of  the  present  day,  only  larger.  Such  was  the  condition 
of  the  beds  that  are  now  coal  in  the  Coal  formation. 
Many  coal  beds  contain  stumps  of  trees  rising  out  of  the 
coal  (Fig.  25);  and  they  always  stand  perpendicularly 
to  the  bed,  however  much  the  latter  may  be  displaced, 
showing  that  the  bed  was  horizontal  when  it  was  formed, 
or  when  the  trees  were  growing. 

Exceptions   to  a  Horizontal  Position.  —  When   a   river 
empties  into  a  lake  or  sea,  the  bottom  of  which,  near  its 
FIG.  25.  mouth,  is  more  or  less  inclined,  the 

deposits  of  detritus  made  by  the  river 
will  for  a  while  conform  to  the  slope 
of  the  bottom,  as  in  Fig.  26.  When 
a  river  falls  down  a  precipice,  it  makes 
a  steep  bank  of  earth  at  the  foot,  whose 
coai  beds  with  fossil  stumps.  iayers?  if  aiiy  are  made,  have  the  slope 

of  the  bank.  In  beach-made  deposits  the  layers  have  the 
slope  of  the  beach  (page  154).  But  these  and  similar  cases 
of  exceptions  to  a  horizontal  position  are  of  small  extent. 

2.  Dislocations  of  Strata.  —  Most  of  the  strata  of  the 
globe  have  lost  their  original  horizontal  position  so  as 
to  be  more  or 
less  inclined;  and 
some  are  even  ver- 
tical. They  are 
occasionally  bent 
or  folded,  as  a 
quire  of  paper  might  be  folded,  only  the  folds  are  miles, 
or  scores  of  miles,  in  sweep. 

They  have  often  also  been  fractured,  and  the  separated 
parts  have  been  pushed,  or  else  have  fallen,  out  of  their 
former  connections,  so  that  the  portion  of  a  stratum  on 
one  side  of  a  fracture  is  often  inches,  feet,  or  even  miles, 
above  that  on  the  other  side. 

The  maximum  thickness  of  stratified  rocks  is  said 
to  be  over  25  miles,  though  only  a  part  of  this  thick- 


Fifi.  26. 


Inclined  strata  deposited  on  a  steep  slope. 


ROCK  MASSES,   OR   TERRANES. 


51 


FIG.  2T. 


ness  exists  in  any  one  region  (pages  42,  224).  If  the  strata 
were  all  in  their  original  horizontal  position,  it  is  evident 
that  no  such  thickness  of  strata  could  be  within  the  reach 
of  observation.  The  maximum  thickness  of  strata  ob- 
servable under  such  conditions  would  be  limited  by  the 
height  of  cliffs  formed  by  erosion,  or  by  the  depth  of  arti- 
ficial borings.  But  the  up- 
turning which  the  earth's 
crust  has  undergone  has 
brought  the  edges  of  strata 
to  the  surface,  and  there  is 
hence  no  such  limit :  how- 
ever deep  stratified  beds 
may  extend,  there  is  no  outcrop, 

reason    why    the    whole 

should  not  be  brought  up  so  as  to  be  exposed  to  view  in 
some  parts  of  the  earth's  surface. 

The  following  are  explanations  of  the  terms  used  in 
describing  the  positions  of  strata:  — 

Outcrop.  —  The  portions  or  ledges  of  strata  projecting 
out  of  the  ground,  or  in  view  at  the  surface  (Fig.  27). 

Dip.  —  The  slope  of  inclined  or  tilted  strata.  In 
Figs.  27,  28,  dp  is  the  direction  of  the  dip.  Both  the 

angle  of  slope  (i.e., 
the  angle  between 
the  plane  of  stratifi- 
cation and  a  horizon- 
tal plane),  and  the 
direction  with  refer- 
ence to  points  of  com- 
pass, are  noted  by  the 
geologist:  thus,  it  may 
be  said  of  beds,  the 
dip  is  50°  to  the  south,  or  5°  to  the  northwest,  etc. 

When  only  the  edges  of  layers  are  exposed  to  view,  it 
is  not  safe  to  take  the  slope  of  the  edges  as  the  slope  of 
the  layers  ;  for,  in  Fig.  28,  the  edges  on  the  faces  1,  2,  3,  4 


Sections  showing  true  and  false  dips. 


52 


STRUCTURAL  GEOLOGY. 


FIG.  29. 


are  all  edges  of  the  same  beds,  and  only  those  of  the  face 
1  would  give  the  right  dip. 

The  dip  is  measured  by  means  of  instruments  called 
clinometers.  In  Fig.  29,  abed  represents  a  square  block 
of  wood,  having  a  graduated  arc  be,  and  a  plummet  hung 
below  a.  Placed  on  the  sloping  surface  AB,  the  position  of 
the  plummet  gives  the  angle  of  dip.  This  kind  of  clinom- 
eter is  often  made  in  the  form  of  a  watch,  and  combined 
with  a  compass.  It  is  most  convenient  for  use  when  it 
has  a  square  base.  One  like  that  figured  is  easily  made 

out  of  a  piece  of 
board  ;  it  may  be  3 
to  4  inches  on  a  side, 
and  about  half  an 
inch  thick.  To  avoid 
errors  from  the  un- 
evenness  of  a  rock,  a 
board  mav  be  laid 

Measurement  of  dip,  by  clinometer.  » 

down   first,   and    the 

measurement  be  made  on  its  surface.  But,  if  the  instru- 
ment has  a  square  base,  it  is  often  best  to  measure  the  dip 
by  holding  it  between  the  eye  and  the  rock,  with  one 
edge  of  the  base  in  the  direction  of  the  dipping  layers. 
Strike.  —  The  horizontal  direction  at  right  angles  with 
the  dip.  In  Fig.  27,  the  dotted  line  st  represents  the 
direction  of  the  strike.  It  is  measured  by  means  of  a 
small  compass,  which  usually  forms  part  of  the  clinometer. 
Such  a  compass  may  be  set  in  a  clinometer  made  like  the 
one  shown  in  Fig.  29.  It  need  not  be  central  in  the 
square,  but  should  have  the  meridian  line  parallel  to  one 
of  the  four  sides.  If  the  edges  of  the  layers  in  view  over 
a  ledge  are  in  any  part  quite  horizontal,  the  direction  of 
those  edges  will  give  the  true  strike  ;  but,  if  they  are  at 
all  inclined,  the  direction  of  a  horizontal  line  must  be  de- 
termined on  the  surface  of  one  of  the  layers.  The  cli- 
nometer may  be  used  also  for  measuring  the  dip  of  rocks 
that  are  rods  distant,  and  the  slopes  of  distant  mountains. 


ROCK  MASSES,   OR  TERRANES. 


53 


Faults.  —  In  the  making  of  faults  (aa,  bb,  Fig.  30), 
there  is  a  fracturing,  and  a  shoving  up  or  down  of  the 
beds  on  one  side  of  the  fracture;  „  FIG.  so. 

that  is,  a  downthrow  on  one  side 
.or  an  upthrow  on  the  other.  The 
amount  of  displacement  is  the 
amount  of  fault ;  it  may  be  a 
foot  or  less,  or  10,000  feet  or 
more.  The  friction  attending 
the  movement  may  cause  a  bend- 
ing of  the  layers  in  contact,  as  along  the  line  bb,  in  Fig.  30. 
The  deepest  fractures  and  faults  have  been  produced  in 
connection  with  the  making  of  mountains. 

Folds  or  Flexures.  —  Folds  or  flexures  in  strata  are  rep- 
resented in  Fig.  31,  A,  B  ;  and  in  the  natural  sections 


Anticlines  and  synclines. 

Figs.  206-209,  pages  212,  213,  from  the  Appalachian  Moun- 
tains, a  region  of  numerous  flexures  on  a  grand  scale,  as 
well  as  of  many  faults  ;  some  flexures  having  a  span  of 
several  miles,  and  others  of  only  a  few  feet  or  inches. 

In  Fig.  31,  A,  ax  represents  the  axial  plane  of  the  fold, 
and  the  intersection  of  the  surface  of  the  strata  by  that 
plane  is  the  axis  of  the  fold. 

The  flexure  very  often  has  one 
side  steeper  than  the  other,  as  illus- 
trated above.     In  some  regions,  the 
overturned  folds.  P™h  by  which  it  was  made  was 

continued  until  the  strata  became 

vertical ;  and,  further  still,  until  the  top  was  pressed  over 
beyond  the  vertical,  and  fold  of  this  kind  followed  fold,  as 
illustrated  in  Fig.  32.  In  more  extreme  cases,  the  push 


FIG.  32. 


54 


STRUCTURAL  GEOLOGY. 


was  continued  until  there  was  produced  a  complete  inver- 
sion of  the  beds,  as  is  represented  in  Fig.  33,  a  section 
of  the  Dent  de  Morcles,  near  Martigny  in  Switzer- 
land, by  Golliez.  The  length  of  the  section  is  about 
five  miles;  and  the  horizontal  and  the  vertical  scale  of 
the  figure  are  equal.  The  horizontal  line  at  the  base  of 
the  figure  represents  the  level  of  the  sea.  The  stratum  9, 
which  before  the  folding  was  the  uppermost  stratum,  is 
folded  back  on  itself ;  and  8,  7,  and  6,  which  were  origi- 
nally underlying  strata,  now  overlie  it,  upside  down.  It 
is  seen  that  the  strata  6  and  7  are  present  only  in  the 
overturned  part  of  the  fold;  these  beds  must  have  ex- 

FIG.  33. 


N.W. 


S.E. 


Section  of  the  Dent  de  Morcles.  —  1,  Metamorphic  rocks  ;  2,  Carboniferous  ;  3,  Triassic  ; 
4,  Lower  Jurassic  (Lias  and  Dogger) ;  5,  Upper  Jurassic  (Malm) ;  6,  Lower  Cretaceous 
(Neocomian);  7,  Upper  Cretaceous;  8,  Lower  Eocene  (Numinulitic) ;  9,  Upper  Eocene. 

tended  northwestward  between  5  and  8,  but  they  have 
been  pinched  out  in  the  lower  limb  of  the  fold  by  the  tre- 
mendous pressure  to  which  the  rocks  have  been  subjected. 
At  the  extreme  left  of  the  figure,  stratum  6  is  seen  in  its 
normal  position  overlying  5. 

Flexures  often  have  fractures  somewhere  along  the 
bend  ;  and  the  fractures  are  often  lines  of  fault. 

Anticline. — An  upward  arching  of  the  strata,  which 
slope  away  from  the  axial  plane  in  opposite  directions, 
as  the  layers  either  side  of  ax  in  Fig.  31,  A  :  the  axis  is 
here  called  an  anticlinal  axis.  The  word  anticline  is 


ROCK  MASSES,   OB   TERRANES.  55 

from  the  Greek  air/,  iu  opposite  directions,  and  K\LVO),  to 
incline. 

Syncline.  —  A  downward  bend,  the  strata  sloping  toward 
the  axial  plane.  In  Fig.  31,  B,  the  axes  corresponding 
to  ax,  ax,  are  anticlinal  axes,  that  corresponding  to  a'x', 
between  the  others,  a  synclinal  axis.  The  word  syncline 
is  from  the  Greek  avv,  together,  and  K\LVCO. 

Monocline.  —  A  form  of  flexure  in  which  the  strata  slope 
in  only  one  direction,  as  when  a  series  of  strata  is  elevated 
(relatively)  in  one  area  and  depressed  in  an  adjacent  area 
without  fracture.  Such  monoclinal  flexures  pass  by  fine 
gradations  into  faults.  A  series  of  strata  having  an 
apparently  monoclinal  attitude  may  be  only  a  part  of 
an  anticline  or  syncline  of  which  the  other  side  is  con- 
cealed. The  word  monocline  is  from  the  Greek  /-to'z/os, 
one,  and  K\IVCO. 

Geanticline,  Greosyncline.  —  Bendings  of  the  earth's  crust, 
geanticline  an  upward  bend,  and  geosyncline  a  downward 
bend.  These  words  are  from  the  Greek  yrj,  earth,  and  the 
words  anticline  and  syncline. 

In  ordinary  synclines  and  anticlines,  the  flexures  involve 
a  varying  thickness  of  strata,  the  arches  have  a  span  of 
a  few  miles  at  most,  and  the  height  of  the  arches  bears 
generally  a  large  ratio  to  the  width.  In  geanticlines  and 
geosynclines,  the  earth's  crust  is  affected  to  a  much 
greater  depth  (extending  much  below  the  stratified  por- 
tion, or  supercrust),  the  arches  have  a  span  of  scores  or 
hundreds  of  miles,  and  the  height  of  the  arches  is  very 
small  in  comparison  with  their  width.  Within  the  limits 
of  a  single  geanticline  or  geosyncline,  there  may  be  a 
number  of  alternating  anticlines  and  synclines. 

The  subject  of  flexures  and  faults  is  best  studied  by 
making  models  out  of  sheets  of  moist  clay  (or  better  of 
paraffin  containing  a  little  beeswax),  using  lampblack 
and  red  and  yellow  ocher  for  coloring  the  different  beds, 
and  then  making  cross  sections. 

Effects  of  Denudation  on  Flexed   or   Upturned  Hocks; 


56 


STRUCTURAL   GEOLOGY. 


FIG.  34. 


Fio.  35. 


123    32 


Decapitated  Folds.  —  If  the  top  of  the  fold  in  Fig.  34  were 
cut  off  at  ab,  there  would  remain  the  part  represented  in 
Fig.  35,  in  which  there  is  no  appearance  of  any  fold,  and 

only  a  uniform  series  of  dips ; 
and,  although  1',  2',  3',  appear  to 
be  the  lower  strata  of  the  series, 
they  are  actually  parts  of  1,  2, 
3.  A  long  series  of  such  folds 

seaums  showing  effect'of  decked    pressed  together,  and  then  decap- 
folds-  itated,  would  make  a  series  of  uni- 

form dips  (an  apparently  monoclinal  structure)  over  a  wide 
extent  of  country  (see  Fig.  32). 

The  true  succession  has  been  further  obscured  by  the 
removal  of  the  beds  over  great  areas  and  the  filling  up  of 
intermediate  depressions  by  soil ;  so  that  the  rocks  are 
visible  only  at  long  intervals  (as  in  Fig.  36).  Many  of  the 
difficulties  in  the  study  of  rocks  arise  from  this  cause. 

Fro.  36. 


Section  showing  discontinuity  of  outcrops. 

Unconformable  Strata.  — When  strata  have  been  ele- 
vated (usually  with  more  or  less  tilting  or  folding),  and, 
after  more  or  less  erosion,  have  been  again  depressed 
below  the  water  level,  and,  subsequently,  horizontal  beds 
have  been  laid  down  over  them,  the  two  sets  are  said  to 
be  unconformable.  Thus,  in  Fig.  37,  the  beds  ef  are  un- 
conformable  both  with  the  tilted  beds  cd  and  with  the 
folded  beds  ab  ;  so  also  the  tilted  beds  cd  are  uncomforin- 
able  with  those  beneath. 

It  is  plain  that  the  folded  rocks  ab  are  the  oldest,  and 
that  the  folding  took  place  before  the  overlying  beds  were 
deposited.  Again,  it  is  evident  that  the  beds  cd  are  older 
than  the  beds  ef,  and  also  that  they  were  tilted  and  faulted 
before  the  latter  were  formed.  Supposing  the  uppermost 
of  the  folded  rocks  ab  were  of  Carboniferous  age,  and  the 
tilted  beds  cd  were  Triassic,  the  geologist  would  conclude 


HOCK  MASSES,   OR   TERRANES. 


57 


that  the  upturning  and  folding  of  the  earlier  rocks  occurred 
after  the  deposit  of  the  Carboniferous  strata  and  before 
that  of  the  Triassic.  In  like  manner,  if  the  horizontal 
strata  ef  were  Cretaceous,  the  time  of  the  tilting  and 
faulting  of  the  beds  cd  would  be  shown  to  be  between 
the  Triassic  and  the  Cretaceous. 

The  special  significance  of  unconformability  in  the  inter- 
pretation of  the  geological  record,  is  that  it  always  marks 
an  interval  of  time  during  which  (in  the  region  in  ques- 
tion) no  rocks  were  formed.  The  two  sets  of  strata  may 

FIG.  37. 


o 


Unconformable  strata. 

be  richly  fossiliferous,  and  so  bear  testimony  in  regard  to 
the  history  of  life  in  their  respective  periods.  But,  for  the 
interval,  long  or  short,  in  which  the  older  series  of  strata 
was  above  the  water  level,  and  was  undergoing  erosion, 
there  is,  at  least  locally,  a  gap  in  the  record. 

Overlap  is  the  name  given  to  the  condition  which  exists 
when  the  sea,  after  depositing  a  series  of  strata,  has  spread 
more  widely  over  the  land,  and  has  deposited  another 
series  of  beds  with  these  new  limits.  These  changes  of 
sea  level  were  going  forward  during  the  progress  of  mosi. 
formations,  and,  consequently,  overlap  should  be  common, 
though  not  always  easily  distinguished. 


THE  ANIMAL  AND  VEGETABLE  KINGDOMS. 

SINCE  life  has  been  an  important  agent,  dynamically,  in 
Geology,  and  its  history  constitutes  a  chief  part  of  the 
historical  branch  of  the  science,  some  knowledge  of  the 
various  kinds  of  animals  and  plants  is  of  the  highest  im- 
portance to  the  student.  A  brief  review  of  the  classifica- 
tion of  the  animal  and  vegetable  kingdoms,  and  of  the 
distribution  of  life  over  the  globe,  is  here  introduced. 

CLASSIFICATION. 

Distinctions  between  an  Animal  and  a  Plant.  —  A  typical 
animal  (1)  is  sustained  by  nutriment  taken  into  its  inte- 
rior for  digestion  and  assimilation.  (2)  It  is  capable  of 
perceiving  the  existence  of  other  objects,  through  one  or 
more  senses.  (3)  It  has  (except  in  some  of  the  lower 
species)  a  head,  in  which  are  the  principal  nerve  centers 
controlling  voluntary  motion,  and  the  mouth.  (4)  It  is 
fundamentally  a  fore-and-aft  structure,  the  head  being 
the  anterior  extremity ;  and  it  is  typically  forward- 
moving.  (5)  With  its  growth  from  the  germ,  there  is 
an  increase  in  mechanical  power  until  the  adult  size  is 
reached.  (6)  In  the  process  of  respiration,  it  uses  oxy- 
gen and  gives  out  carbonic  acid.  (7)  It  finds  nutriment 
only  in  organic  materials,  or  tissues  of  plants  or  animals ; 
never  in  mineral  material. 

A  plant  (1)  is  sustained  by  nutriment  taken  into  the 
tissues  by  absorption  at  the  surface.  (2)  It  is  incapable 
of  perception,  having  no  senses.  (3)  It  has  no  head,  no 

68 


CLASSIFICATION.  59 

power  of  voluntary  motion,  no  mouth.  (4)  It  is  funda- 
mentally an  up-and-down,  structure,  and,  with  few  excep- 
tions, fixed.  (5)  In  its  growth  from  the  germ  or  seed, 
there  is  no  increase  of  mechanical  power.  (6)  In  the 
process  of  nutrition,  ordinary  plants  use  carbonic  acid, 
and  give  out  oxygen  with  only  an  extremely  small  amount 
proportionally  of  carbonic  acid.  The  Fungi,  and  some 
other  plants  that  are  not  green,  are  an  exception,  using 
oxygen,  and  giving  out  much  carbonic  acid.  (7)  A  plant 
finds  nutriment  in  mineral  material,  from  which  it  makes 
organic  tissues. 

The  Animal   Kingdom. 

The  nature  of  an  animal  requires,  for  a  full  exhibition 
of  its  powers,  the  following  parts  :  — 

1.  A  stomach  and  its  appendages,  to  turn  the  food  into 
blood,  with  an  arrangement  for  carrying  off  refuse  mate- 
rial. 

2.  A  system  of  vessels  for  carrying  this  blood  through- 
out the  body,  so  as  to  promote  growth  and  a  renewal  of 
the  structure. 

3.  A  heart,  or  forcing  pump,  to  send  the  blood  through 
the  vessels. 

4.  A  means  of  respiration,  or  of   taking  oxygen  into 
the  system  (as  by  lungs  or  gills),  since  the  energy  of  the 
body  is  derived  from  the  combination  of  oxygen  with  the 
elements  contained  in  the  food. 

5.  Muscles,  or  contractile  fibers,  to  put  the  parts  or 
members  in  motion  by  their  contraction. 

6.  A  brain,  or  head  mass  of  nervous  matter,  to  serve 
as  a  seat  of  sensation  and  volition,  and  a  system  of  nerves 
to  convey  sensory  impressions  to  the   brain  and   motor 
impulses  to  the  muscles. 

In  the  lowest  forms  of  animal  life,  as  some  microscopic 
Protozoans,  the  stomach  is  not  a  permanent  cavity,  but 
is  formed  in  the  mass  of  the  tissue  whenever  and  wherever 
a  particle  of  food  comes  in  contact  with  the  body.  In 


60  THE   ANIMAL   AND    VEGETABLE   KINGDOMS. 

other  words,  a  stomach  is  extemporized  as  it  is  needed. 
Animals  of  a  little  higher  grade,  as  Anthozoans,  have  a 
mouth  and  a  stomach,  muscles,  an  imperfect  nervous  sys- 
tem, and  a  means  of  respiration  through  the  general 
surface  of  the  body ;  but  there  is  no  heart,  and  the  animal 
is  ordinarily  fixed  to  a  support. 

The  subkingdoms,  or  primary  divisions  of  the  animal 
kingdom,  most  commonly  recognized  at  present  by  zoolo- 
gists, are  the  following  :  — 

1,  PROTOZOANS  ;  2,  SPONGES  ;  3,  CCELENTERATES  ;  4, 
ECHINODERMS  ;  5,  MOLLUSCOIDS  ;  6,  MOLLUSKS  ;  7,  VER- 
MES,  or  WORMS  ;  8,  ARTHROPODS  ;  9,  TUNIC ATES  ;  10, 

VERTEBRATES.1 

1.  PROTOZOANS. 

The  name  Protozoans  is  derived  from  Greek  TT/JWTO?, 
first,  and  ftwoz/,  animal,  and  accordingly  signifies  the 
simplest  and  lowest  of  animals.  According  to  the  mod- 
ern doctrine  of  evolution,  some  representatives  of  this 
group  must  have  been  the  first  of  animals  in  time,  and 
the  ancestors  of  all  more  complex  forms.  The  Protozoans 
are  characterized  by  their  extreme  simplicity,  the  minute 
body  consisting  strictly  of  a  single  cell.  The  Protozoans 
that  form  communities  by  continuous  budding  or  fission, 
and  thus  come  to  form  masses  of  some  size,  constitute 
only  an  apparent  exception  to  the  above  statement. 

1  This  classification  is  provisionally  adopted  as  a  matter  of  convenience, 
since  it  is  believed  to  be  used  more  generally  than  any  other  in  recent 
manuals  of  zoology,  though  it  does  not  precisely  express  the  views  of  the 
editor.  In  former  editions  of  this  work,  the  Sponges  were  included 
among  the  Protozoans ;  the  Coelenterates  and  Echinoderms  were  united 
under  the  name  Radiates;  the  Molluscoids,  Mollusks,  and  Tunicates 
were  united  under  the  name  Mollusks  ;  and  the  Vermes  and  Arthropods 
were  united  under  the  name  Articulates.  In  the  latest  edition  of  the 
Manual,  the  Ccelenterates  and  Echinoderms  are  united  under  the  name 
Radiates ;  the  Molluscoids,  Mollusks,  and  (doubtfully)  a  part  of  the 
Vermes  are  united  under  the  name  Non-Articulates ;  and  the  remainder 
of  the  Vermes  and  the  Arthropods  are  united  under  the  name  Articu- 
lates. 


CLASSIFICATION. 


61 


There  is  in  these  creatures  nothing  like  the  development 
of  the  higher   animals,  in  which   the  egg   (originally  a 


FIGS.  38-51. 


FORAMINIFERS  :  Fig.  38,  Orbuliiia  universa ;  39,  Globigerina  rubra ;  40,  Textularia  globu- 
losa;  41,  Rotalia  globulosa;  41  a,  side  view  of  Kotalia  Boucana;  42,  Grammostomum 
phyllodes  ;  43,  a,  Frondicularia  annularis  ;  44,  Triloculina  Josephina ;  45,  Nodosaria  vul- 
garis  ;  46,  Lituola  nautiloides  ;  47,  a,  Flabellina  rugdsa ;  48,  Chrysalidina  gradata ;  49,  «, 
Cuneolina  pavonia ;  50,  Nummulites  nummularia ;  51  a,  &,  Fusulina  cylindrica. 

single  cell,  like  a  Protozoan)  comes  to  be  divided   into 
numerous  cells,  of  which  the  various  tissues  of  the  body 

FIG.  52. 


FORAMINIFER  :  Globigerina  bulloides. 

are  formed.  Some  of  these  minute  creatures  form  cal- 
careous or  siliceous  skeletons,  and  are  therefore  capable 
of  preservation  as  fossils. 


62 


THE   ANIMAL   AND   VEGETABLE   KINGDOMS. 


FIG.  53. 


FORAMINIFER  :  Eotalia,  with  pseu- 
dopods  protruded. 


Of  the  classes  of  Protozoans,  only  one  is  of  any  impor- 
tance in  Geology,  —  the  Rhizopods. 

Rhizopods.  —  The  name  is  derived  from  the  Greek 
pi^a,  root,  and  TTOU?,  foot,  and  re- 
fers to  the  power  which  the  ani- 
mal possesses  of  protruding  the 
jelly-like  protoplasm  of  which  the 
body  is  composed,  into  temporary 
processes,  often  slender  and  branch- 
ing like  little  roots.  These  tem- 
porary extensions  of  the  body, 
called  pseudopods  (Greek  i/reuS^, 
false,  and  TTOU?,  foot),  envelop 
particles  of  food,  and  serve  as 
extemporaneous  stomachs  for  its 
digestion.  The  power  of  extending  the  protoplasm  of 
the  body  in  various  directions  enables  the  creature  to 
move  with  a  sort  of  flowing  movement. 

Two  groups  of  Rhizopods  are  especially  important  in 
Geology,  —  the  Foraminifers  and 
the  Radiolarians.  The  Foramini- 
fers (Latin  foramen,  in  allusion 
to  the  minute  pores  in  the  shell 
through  which  the  pseudopods 
are  protruded)  have  generally 
calcareous  shells.  A  number  of 
the  shells  are  represented  in 
Figs.  38-51.  Figs.  50,  51  are 
of  natural  size,  and  a  few  Fora- 
minifers have  shells  even  larger 
than  these.  The  others  are  mag- 
nified, most  of  the  shells  being  no  larger  than  grains  of 
sand.  Fig.  52  represents  (much  enlarged)  the  common 
species  of  Grlobigerina,  which  lives  at  the  surface  of  the 
ocean  over  wide  areas,  and  whose  dead  shells  accumulate 
in  the  ooze  at  the  bottom.  As  shown  in  the  figure,  the 
shell,  when  alive  or  unbroken,  is  covered  with  radiating 


FIG.  54. 


KADIOLARIAN  :  Xipbacantha,  x  50. 


CLASSIFICATION. 


63 


57 


FIGS.  58-72. 


spines.      Fig.  53  represents  another  living  species  (also 
much  enlarged),  showing  the  pseudopods  extended. 

The    Radiolarians    (Latin    radius,   in   allusion    to   the 

radiated  arrangement 
of  the  pseudopods)  are 
somewhat  more  highly 
organized  than  the  For- 
aminifers,  the  proto- 
plasm of  their  bodies 
showing  more  indica- 

RADIOLAKIANS  :  Fig.  55,  Lychnocanium ;  56,  Eu-      tion     of      differentiation 
cyrtidium :  57.  Halicalyptra.  •     ,  rp\i  i 

into  parts.      They  have 

siliceous  skeletons,  which  are  often  exquisitely  beautiful. 
Some  of  them  are  rep- 
resented, considerably 
magnified,     in     Figs. 
54-57. 


2.  SPONGES. 

The  Sponges  show 
a  higher  grade  of  or- 
ganization   than    the 
Protozoans,  since 
they  produce  true 
eggs,    which    di- 
vide   into     numerous 
cells  in  the  process  of 
development.       They 
attain,     however,     no 
such  degree  of  differ- 

Pntiatinn  of  ti<i<mp<j  anrl  SPONGE  SPICULES:  Figs.  58-61,  Geodia  or  allied  genera; 

62,  globostellate  spicule,  related  to  Geodia  ;  63,  Stel- 
letta ;  64,  Carterella ;  65,  66,  Tetractinellid  spicules ; 
67,  Ventriculites ;  68,  Eagadinia  annulata;  69,  Tisi- 
phonia ;  70,  the  same  ;  71,  Kacodiscula ;  72,  Plintho- 
sella  squamosa.  Figs.  62,  65,  66,  x  10;  68,  x  68; 
others,  x  34.  Hinde. 


organs  as  is  shown  in 
the  higher  animals. 
The  gelatinous  body 
of  a  sponge  is  trav- 
ersed by  a  system  of  canals,  to  which  the  sea  water  is 


64  THE    ANIMAL   AND    VEGETABLE   KINGDOMS. 

admitted  by  numerous  minute  pores,  and  from  which  it 
is  discharged  through  a  smaller  number  of  larger  orifices. 
In  most  Sponges  the  gelatinous  body  is  supported  by  a 
network  of  horny  fibers,  generally  associated  with  minute 
spicules  of  silica.  The  sponges  used  in  bathing  are  the 
horny  skeletons  of  species  which  are  destitute  of  siliceous 
spicules.  In  some  Sponges  the  skeleton  is  entirely  com- 
posed of  siliceous  spicules,  and  still  others  have  a  cal- 
careous skeleton.  The  spicules  of  Sponges  have  various 
forms,  as  shown  in  Figs.  58-72. 

3.  CCELENTERATES. 

The  name  is  derived  from  #04X09,  hollow,  and  evrepov, 
intestine,  and  refers  to  the  fact  that  in  these  animals  the 
only  cavity  is  the  digestive  cavity,  there  being  no  body- 
cavity,  or  peri  visceral  cavity,  such  as  is  found  in  the 
higher  animals.  By  the  possession  of  a  distinct  mouth 
and  digestive  cavity,  the  Coelenterates  show  a  higher 
grade  than  the  preceding  groups.  Rudiments  also  of  a 
nervous  system  appear.  The  mouth  is  generally  sur- 
rounded by  a  wreath  of  radiating  tentacles,  and  in  most 
species  all  the  organs  are  repeated  in  radial  order. 

Two  of  the  classes  of  Coelenterates  are  important  in 
geology,  —  1,  Hydrozoans  ;  2,  AntTiozoans. 

1.  Hydrozoans. — The  name  (from  Greek,  v$pa,  hydra,  and 
ftwoy,  animal)  denotes  animals  resembling  the  little  fresh- 
water hydra.  In  that  little  creature  (Fig.  73)  the  body 
is  little  more  than  a  tube,  with  the  opening  of  the  mouth 
at  one  end,  surrounded  by  a  wreath  of  tentacles.  Fig.  74 
represents  a  somewhat  similar  marine  form.  In  many 
cases  communities  are  formed  by  budding,  the  succes- 
sively formed  individuals  (zooids)  remaining  permanently 
attached  to  each  other.  These  communities  are  often 
branching,  and  look  like  delicate  seaweeds.  They  are 
often  inclosed  in  a  delicate  horny  investment.  Two  of 
these  horny  skeletons  are  shown  in  Figs.  75,  76.  A  few 


CLASSIFICATION. 


65 


(as  Millepore)  form  a  calcareous  skeleton  or  coral.  Other 
Hydrozoans,  called  Jellyfishes,  or  Medusae,  have  the 
gelatinous  body  disk-shaped  or  hemispherical,  and  swim 
freely  with  the  mouth  downward.  A  Medusa  is  shown  in 
Fig.  77.  In  many  species,  Medusae  are  produced  by  bud- 
ding from  a  colony  of  hydra-like  zooids.  In  this  case  the 
Medusa  produces  eggs,  from  which  the  Hydroid  com- 
munity is  developed.  This  alternation  of  generations  is 
very  common  among  Hydrozoans,  and  occurs  in  some 
other  classes  of  animals. 


HYDROZOANS  :    Fig.   73,  Hydra,  x  8 ;    74,    Syncoryne ;    75,  Sertularia  abietina ;    a,    same, 
magnified ;  76,  Sertularia  rosacea ;   a,  same,  magnified ;  77,  Tiaropsis. 

2.  Anthozoans. — The  name  (from  Greek  aV0o?,  flower, 
and  fwoz/,  animal)  refers  to  the  beautiful  flower-like  aspect 
given  to  many  of  these. creatures  by  their  tentacles,  which 
radiate  like  the  petals  of  a  flower  (Figs.  78,  79,  81),  and 
which  are  often  brightly  colored.  Anthozoans  are  dis- 
tinguished from  Hydrozoans  by  having  an  involution  of 
the  body  wall  at  the  mouth,  forming  a  short  esophagus 
leading  into  the  main  cavity  or  stomach  ;  and  by  hav- 
ing the  latter  cavity  partly  divided  into  radiating  cham- 
bers by  partitions  extending  inward  from  the  body  wall. 
Most  of  the  Anthozoans  form  communities,  branching 
(Fig.  79),  incrusting,  or  massive  (Fig.  80),  by  budding  or 


66 


THE   ANIMAL   AND   VEGETABLE   KINGDOMS. 


fission.  Some  Anthozoans,  as  the  Sea  Anemone  (Fig.  78), 
have  no  hard  parts.  Most  of  them,  however,  form  corals 
by  the  deposit  of  calcareous  material  in  some  part  of  the 
body  wall,  and  in  radiating  plates  (septa)  extending  into 
the  radiating  chambers.  These  radiating  plates  cause  a 
coral  to  be  marked  by  stars  (one  corresponding  to  each 
zooid  in  the  community),  as  shown  in  Fig.  80,  which  rep- 
resents a  piece  of  fossil  coral.  Most  of  the  coral  animals 
belong  to  the  group  of  Zoantharians,  in  which  the  ten- 
tacles and  other  radiating  parts  are  indefinite  in  number 


ANTHOZOANS  :  Fig.  78,  Actinia ;  79,  Dendrophyllia ;  80,  Isastraea  oblonga ;  81,  Gorgonia. 

(Figs.  78,  79),  and  usually  in  multiples  of  six.  In  the 
remarkable  fossil  group  of  CyathophyUoids,  the  parts  were 
in  multiples  of  four.  The  Precious  Coral  and  the  Sea 
Fans  (  Grorgonians),  with  their  peculiar  horny  skeletons,  be- 
long to  the  Alcyoniarians,  in  which  the  tentacles  (Fig.  81) 
are  uniformly  eight  in  number  and  pinnate  in  form. 

4.  ECHINODERMS. 

The  name  is  derived  from  Greek  e^vo?,  hedgehog,  and 
SejOyLta,  skin,  and  refers  to  the  armor  of  spines  with  which 
many  of  the  species  are  covered  (Fig.  8.7).  The  Echino- 
derms  differ  from  the  Coelenterates  in  having  a  distinct 
body-cavity,  or  perivisceral  cavity,  within  which  the  ali- 
mentary canal  is  contained.  They  show  also  a  nervous 


CLASSIFICATION. 


67 


system  much  more  highly  developed,  consisting  of  a 
nervous  ring  around  the  mouth  and  radiating  nerves 
passing  to  the  several  segments  of  the  body.  As  in  the 
Coelenterates,  the  organs  of  the  body  in  general  are 
radially  repeated.  The  number  of  radial  segments  is  gen- 
erally five.  In  some  Echinoderms,  the  radial  segments 
are  very  unequally  developed,  and  the  radial  symmetry 
gives  place  in  large  degree  to  a  bilateral  symmetry. 

Four  of  the  classes  of  Echinoderms  have  considerably 
developed  external  skeletons,  and  are  important  in  Geol- 
ogy :  —  1,  Crinoids  ;  2,  Ophiuroids  ;  3,  Asterioids  ;  4,  JSchi- 
noids. 


FIGS.  82-84. 


CRINOIDS  :  Fig.  82,  Callocystites  Jewettii ;  83,  Pentremites  pyriformis ;  84,  Encrinus  lilii- 

formis. 

1.  Crinoids.  —  The  name  is  from  Greek  Kplvov,  lily,  and 
many  of  the  species  have  been  commonly  called  Stone-lilies. 
The  species  shown  in  Fig.  84  is  named  the  Lily  Encrinite. 
Unlike  all  other  Echinoderms,  they  are  (with  perhaps  a 
few  exceptions)  attached,  at  least  temporarily,  by  a  stem 
of  greater  or  less  length  growing  out  from  the  pole  of 
the  body  opposite  the  mouth.  The  Crinoids  are  a  class 
almost  extinct.  One  of  the  few  living  species  is  repre- 
sented in  Fig.  85.  Two  of  the  three  orders  of  the  class 
(Cystoids  and  Blastoids)  are  entirely  extinct. 

The  Cystoids  have  the  plates  of  the  shell  not  regularly 
radial  in  arrangement,  and  the  arms  either  altogether 


68 


THE   ANIMAL   AND    VEGETABLE   KINGDOMS. 


wanting  or  feebly  developed,  and  not  regularly  radiating. 
One  species  is  represented  in  Fig.  82. 

The  Blastoids  (Greek  /SXacrro?,  bud)  have  an  aspect  of 
which  the  name  is  beautifully  descriptive.  The  plates  of 
the  shell  are  arranged  in  regularly  radial  order.  The 
arms  are  wanting,  but  are  represented  by  five  areas  radiat- 
ing from  the  oral  pole  of  the  shell,  and  bearing  pinnules 
like  those  which  are  borne  on  the  arms  in  the  Brachiates. 
Fig.  83  represents  a  Blastoid. 


FIGS.  85-87. 


CRINOIDS  :  Fig1.  85,  Pentacrinus  capnt-medusse ;  ffl,  ft,  c,  d,  sections  of  stems  of  different 
species  of  Pentacrinus.  —  ASTERIOID  :  Fig.  86,  Palseaster  Niagarensis.  —  ECHINOID  :  Fig. 
.    87,  Echinus,  x  J. 

The  Brachiates  (Latin  brachium,  arm)  have  the  plates 
of  the  shell  and  the  well-developed  arms  arranged  in 
regularly  radial  order.  The  arms  are  typically  five  in 
number,  but  generally  fork  almost  at  the  base,  and  often 
branch  repeatedly,  so  as  to  seem  very  numerous.  Two 
species  are  shown  in  Figs.  84,  85. 

2.  Ophiuroids.  —  The  name  (Greek  6'<^?,  snake,  and 
ovpd,  tail)  refers  to  the  slenderness  and  flexibility  of  the 
rays  which  radiate  from  the  small  central  disk.  Brittle 
Stars  and  Serpent  Stars  are  common  names  of  these 


CLASSIFICATION.  69 

animals.      The   viscera   do   not    extend    into    the    slen- 
der rays. 

3.  Asterioids.  —  The    scientific    name    (Greek    do-rijp, 
star)  is  descriptive  of  the  form  of  the  body,  like  the  com- 
mon name  Starfish.     A  fossil  species  is  shown  in  Fig.  86. 
The  .rays,  or  arms,  blend  with  the  central  disk,  instead  of 
being  sharply  distinguished  from  it,  as  in  the  Ophiuroids ; 
and  the  appendages  of  the  alimentary  canal  and  the  other 
viscera  extend  into  the  rays. 

4.  Echinoids. — The  name  (from  Greek  e'%m>9,  hedgehog) 
refers  to  the  spines,  which  in  some  species  are  large  and 
conspicuous.     In  Fig.  87  they  are  shown  on  the  left  side, 
having  been  removed  from  the  other  side  to  show  the 
arrangement  of  the  plates  of  which  the  shell  is  composed. 
In  most  of  the  Echinoids,  the  plates  are  immovably  articu- 
lated with  each  other,  so  as  to  form  a  rigid  shell.     In  this 
they  differ  from  the  preceding  classes,  in  which  the  plates 
(at  least  in  the  rays)  are  movably  articulated.     The  Echi- 
noids are  usually  spheroidal  or  discoidal  in  form.     They 
are  commonly  called  Sea  Urchins. 

5.  MOLLUSCOIDS. 

The  name  implies  a  resemblance  to  the  Mollusks,  with 
which  the  Molluscoids  were  formerly  confounded.  The 
two  groups  agree  in  the  absence  of  the  radial  repetition 
of  homologous  parts,  which  is  characteristic  of  the  two 
preceding  subkingdoms,  and  in  the  absence  of  the  longi- 
tudinal repetition  of  homologous  parts,  which  is  char- 
acteristic of  many  Vermes  and  of  the  Arthropods  and 
Vertebrates.  The  Molluscoids  differ  from  the  Mollusks 
in  having  a  much  less  strongly  developed  nervous  system; 
in  not  having  particular  parts  of  the  body  specialized  for 
locomotive  and  sensory  functions  (foot  and  head),  as  is 
the  case  in  most  of  the  Mollusks ;  and  in  being  generally 
attached,  while  the  Mollusks  are  generally  locomotive. 
Eminently  characteristic  of  the  Molluscoids  is  a  sort  of 
collar  about  the  mouth  (lophophore) ,  sometimes  nearly 


70  THE  ANIMAL   AND   VEGETABLE   KINGDOMS. 

circular,  sometimes  horseshoe-shaped,  sometimes  produced 
into  a  pair  of  long  arms,  bearing  a  fringe  of  tentacles  or 
cirri. 

The  Molluscoids  include  two  classes,  both  of  which  are 
important  in  geology  :  —  1,  Bryozoans  ;  2,  Brachiopods. 

1.  Bryozoans.  —  The  name  (Greek  ftpvov,  moss,  and  fcSo^, 
animal)  is  prettily  descriptive  of  the  delicate  mosslike 
tufts  which  are  formed  by  many  of  the  communities  of 
these  little  creatures.  They  multiply  by  budding  (as  well 
as  by  producing  eggs),  and  the  communities  thus  formed 
often  greatly  resemble  those  .of  Hydrozoans.  The  ani- 
mals, however,  are  much  higher  in  their  grade  of  or- 
ganization, possessing  an  alimentary 

1*1  1*  *•  i  •     * 

canal  inclosed  in  a  perivisceral  cavity, 
an(^  a  well-developed  nervous  gang- 
lion. The  lophophore  (well  shown 
in  Figs.  88,  89)  is  circular  or  horse- 
shoe-shaped, bears  a  wreath  of  rela- 
tively long  tentacles,  and  is  never 
produced  into  a  pair  of  long  arms. 
The  Bryozoan  communities  are  some- 
time*  Destitute  of  any  hard  parts, 


removed  from  its  cell,  more   j^    generally    secrete    a    horny    or 

enlarged.  J  _  .    ,  * 

calcareous   covering,  which   incloses 

each  zooid  in  a  little  cell.     When  the  skeleton  is  calca- 
reous, it  forms  a  delicate  sort  of  coral. 

2.  Brachiopods.  —  The  name  (from  Greek  fipaxfov,  arm, 
and  Trow,  foot)  refers  to  the  peculiar  development  of  the 
lophophore,  which  in  these  animals  is  produced  into  a  pair 
of  long  fringed  arms,  which  are  spirally  coiled  within  the 
shell.  'In  Fig.  90,  one  of  the  arms  is  extended  beyond  the 
margin  of  the  shell.  Unlike  the  Bryozoans,  the  Brachio- 
pods never  multiply  by  budding.  The  skin  is  produced 
into  two  folds,  one  on  the  dorsal,  and  one  on  the  ventral 
side  of  the  body,  which  secrete  the  two  pieces  of  a  bivalve 
shell.  Brachiopods  were  formerly  confounded  with  the 
Lamellibranchs  among  the  Mollusks  (Clams,  Mussels,  etc.), 


CLASSIFICATION. 


FIG.  90. 


since  these  animals  also  have  bivalve  shells.  The  valves 
in  the  Lamellibranchs  are  right  and  left,  and  are  therefore 
entirely  different  from  those  of  Brachio- 
pods in  their  relation  to  the  body  of  the 
animal.  This  difference  of  position  is 
correlated  with  characteristic  differences 
in  the  form  of  the  shell.  In  Brachiopods 
the  two  valves  are  never  alike,  while  in 
Lamellibranchs  (with  a  few  exceptions, 
as  the  Oyster)  they  are  nearly  or  exactly 
alike.  On  the  other  hand,  each  valve  is 
almost  always  symmetrical  in  the  Brachi- 
opods, never  in  Lamellibranchs.  The 
shells  of  a  number  of  Brachiopods  are 
shown  in  Figs.  91-98.  In  many  Brachiopods,  processes 
are  developed  from  the  interior  of  the  dorsal  valve,  to 

FIGS.  91-98. 


BRACHIOPOD  :    Ehyn- 
chonella  psittacea. 


BRACHIOPODS:  Fig.  91,  Waldheimia  flavescens,  interior  view;  92,  loop  of  Terebratula 
vitrea ;  93,  loop  of  Terebratulina  caput-serpentis  ;  94,  Spirifer  striatus ;  95,  same,  interior 
of  dorsal  valve;  96,  Athyris  concentrica;  97,  Atrypa  reticularis ;  98,  same,  interior  of 
ventral  valve. 

support  the  arms  of  the  lophophore.  These  arm-supports 
may  be  looplike  (Figs.  91-93)  or  spiral  (Figs.  95,  98). 
The  Brachiopods  are  generally  attached  by  a  fleshy  stem 


72 


THE   ANIMAL   AND   VEGETABLE  KINGDOMS. 


FIGS.  99-101. 


passing  out  between  the  valves,  or  (more  commonly) 
through  an  aperture  in  the  beak  of  the  ventral  valve 
(shown  at  a  in  Fig.  96).  In  one  recent  species  of  Lin- 
gula,  the  pedicel  has  been  observed  to  serve  as  an  organ 
of  locomotion.  The  Brachiopods  are  represented  by  but 
few  living  species,  but  were  immensely  abundant  in  early 
geological  periods. 

6.  MOLLUSKS. 

Mollusks  agree  with  the  Molluscoids  in  the  absence  of 
segmentation,  either  radial  or  longitudinal.  They  show, 
however,  a  much  higher  grade  of  organization.  Almost 
always  there  is  a  foot,  or  specialized  loco- 
motive portion  of  the  body;  and  gener- 
ally a  head,  or  specialized  oral  and  sensory 
portion.  The  nervous  system  is  well 
developed.  Special  respiratory  organs  are 
generally  present,  most  commonly  in  the 
form  of  gills.  Budding  is  entirely  un- 
known, reproduction  being  solely  by 
means  of  eggs.  The  integument  is  gener- 
ally produced  into  a  fold,  or  a  pair  of 
folds,  called  the  mantle,  which  secretes  a 
calcareous  shell.  The  shell  is  generally 
large  enough  to  form  a  covering  for  the 
body;  but  is  sometimes  small  arid  con- 
cealed.in  the  mantle,  and  sometimes  rudi- 
99,  cyprina;  ioo,  Tel-  meiitary  or  wanting. 

lina;  101,  Ostrea.  ^»    ,t  -,  *    *r   n       i          ,1 

Or  the  classes  of  Mollusks,  three  are 
important  in  Geology: — 1,  Lamellibranchs ;  2,  Gastro- 
pods; 3,  Cephalopods. 

1.  Lamellibranchs.  —  The  name  (from  Latin  lamella  and 
branchia)  refers  to  the  form  of  the  gills,  which  in  most 
species  are  developed  as  two  lamellar  folds  on  each  side  of 
the  body.  The  Lamellibranchs  differ  from  the  other  classes 
to  be  described,  in  the  lack  of  a  distinct  head,  and  in  the 
lack  of  any  masticatory  apparatus  connected  with  the 


CLASSIFICATION.  73 

mouth.  The  mantle  is  always  developed  in  two  lobes 
(right  and  left),  and  the  shell  accordingly  is  always  bi- 
valve. The  distinctions  between  the  shells  of  the  Lamelli- 
branchs  and  those  of  the  Brachiopods  have  been  given  on 
page  71.  The  interior  of  the  shell  in  Lamellibranchs  bears 
markings  which  give  much  information  in  regard  to  the 
soft  parts  of  the  body.  The  shell  is  generally  closed  by 
two  powerful  muscles,  the  anterior  and  the  posterior  ad- 
ductor. These  make  deep  impressions  where  they  are 
inserted  into  the  shell  (1,  2,  in  Figs.  99, 100).  Sometimes 
(as  in  the  Oyster)  the  anterior  adductor  is  wanting,  and 
then  only  one  impression  is  shown  in  the  shell  (2,  in  Fig. 
101).  In  most  shells  a  somewhat  distinct  line  extends 
from  one  adductor  to  the  other  (jt?jt?,  in  Figs.  99,  100), 
formed  where  the  muscular  border  of  the  mantle  adheres 
to  the  shell.  In  some  species,  the  mantle  lobes  are  entirely 
separate  along  the  ventral  margin,  admitting  the  water 
freely  to  the  gill  chamber.  In  others,  the  mantle  lobes 
are  united  along  the  ventral  margin,  and  their  posterior 
border  is  produced  into  two  tubes  (siphons)  by  which,  re- 
spectively, water  is  admitted  and  expelled.  These  siphons 
are  generally  more  or  less  perfectly  retractile  ;  and  the 
mantle  impression  shows  a  notch,  or  sinus  (s,  in  Fig.  100), 
marking  the  area  into  which  the  siphons  are  withdrawn. 
These  markings  are  often  clearly  shown  in  fossil  shells. 

2.  Gastropods.  —  The  name  (from  yao-Trjp,  belly,  and 
TTOW,  foot)  refers  to  the  fact  that  these  animals  generally 
crawl  on  the  ventral  surface  of  the  flattened  foot,  as  well 
shown  in  Fig.  102,  representing  a  land  Snail.  The  head 
is  supplied  typically  with  two  pairs  of  sensory  tentacles, 
one  of  which  bears  a  pair  of  eyes.  In  the  Snail  (Fig.  102) 
the  eyes  are  borne  on  the  larger  posterior  tentacles.  The 
two  pairs  of  tentacles  may  be  more  or  less  perfectly  fused 
into  a  single  pair.  Respiration  is  generally  effected  by 
means  of  gills ;  but  in  the  land  Snails  there  is  an  air  sack, 
or  simple  lung ;  and  some  Gastropods  have  no  special 
organs  of  respiration.  The  great  majoritv  of  the  Ga«tro- 


74 


THE   ANIMAL   AND   VEGETABLE  KINGDOMS. 


FIG 


pods  have  shells  in  the  form  of  a  turreted  spiral,  large 
enough  to  cover  the  animal  completely.     A  number  of 

fossil  species  are  shown  in 
Figs.  103-108.  Others  have 
shells  flattened,  conical,  or  of 
other  forms.  The  shell  may 
be  small  and  concealed  in  the 
mantle,  or  may  be  entirely 
wanting. 

In   the  Pteropods  (Greek 

oV,  wing,  and  TTOU?,  foot),  regarded  by  most  zoologists 
as  an  aberrant  group  of  Gastropods,  though  perhaps 
deserving  to  be  considered  as  a  distinct  class,  a  pair  of 


GASTROPOD  :  Helix. 


FIGS.  103-108. 


108 


GASTROPODS  :  FIG.   103,   Pyrifusus  Newberryi  ;  104,   105,   Bulla  speciosa  ;  106,  Anchura 
(Drepanocheilus)  Americana  ;  107,  Fasciolaria  buccinoides  ;  108,  Margarita  Nebrascensis. 

lateral  appendages  to  the  foot  are  developed  as  fins  (shown 
in  Fig.   109).      Unlike  most  Mollusks,  these  little  crea- 
tures  are  adapted  for  a  free-swimming,  pelagic    FlG.  10g. 
life.      At  present,  the   Pteropods   include   only 
a  small  number  of  species,  all  of  which  are  of 
very  small  size.     In  early  geological  times  much 
larger  species  existed. 

3.  Cephalopods.  —  The  name  is  from  Greek 
#e(£aX?7,  head,  and  TTOU?,  foot.  In  these  most 
highly  organized  of  Mollusks,  the  head  is  armed  with  a 


Cleodora- 


CLASSIFICATION. 


75 


FIG.  110. 


circle  of  prehensile  tentacles,  and  bears  two  large  eyes 
of  remarkably  elaborate  structure.  Respiration  is  always 
by  means  of  gills.  The  water  taken  into  the  gill  chamber 
is  expelled  through  a  funnel  (shown  at  i  in  Fig.  111). 
The  reaction  of  the  water, 
when  forcibly  ejected,  propels 
the  body  in  the  opposite  di- 
rection, affording  one  of  the 
means  of  locomotion  possessed 
by  these  active  creatures.  The 
Cephalopods  are  divided  into 
two  orders,  both  of  which  have 
played  an  important  role  in 
geological  history. 

The  Tetrabranchs  (Greek 
rerpa,  four,  and  /3pdy%i,a,  gills)  have  four  gills.  Their 
tentacles  are  numerous,  but  not  armed  with  suckers  or 
hooks.  They  have  no  ink-bag.  They  are  defended  by 

FIG.  ill. 


TETKABKANCH  :  Nautilus. 


DIBRANCH:  Loligo  vulgaris,  x  |;  i,  funnel;  p,  pen. 

an  external  shell  :r,  the  form  of  a  tube,  which  may  'be 
straight  or  coiled,  but  which  is  always  divided  into 
chambers  by  transverse  partitions  (septa),  which  are  per- 
forated by  a  smaller  tube  (siphuncle).  Fig.  110  shows 
in  section  the  coiled  and  chambered  shell  of  Nautilus,  the 
only  living  genus  of  the  order. 

The  Dibranchs  (Greek  £&,  twice,  and  ffpdyxia,  gills)  have 
two  gills.  Their  tentacles  are  eight  or  ten  in  number,  and 
bear  suckers  or  hooks,  making  them  very  powerful  weapons. 


76  THE   ANIMAL  AND   VEGETABLE   KINGDOMS. 

They  secrete  an  inky  fluid,  which  is  discharged  through 
the  funnel  when  they  seek  to  escape  from  pursuers.  With 
an  apparent  exception  in  a  single  genus,  they  have  no 
external  shell.  They  generally,  however,  have  some 
sort  of  a  shell  concealed  in  the  mantle.  This  may 
be  the  horny  pen  of  the  Squid  (j?,  in  Fig.  Ill),  the 
so-called  bone  of  the  Cuttlefish,  or  a  chambered  shell 
resembling  the  shells  of  the  Tetrabranchs. 

7.  VERMES,  OR  WORMS. 

The  animals  commonly  included  under  this  name  are 
a  heterogeneous  group.  Some  of  them  have  the  body 
divided  into  a  longitudinal  series  of  segments,  and  the 
nervous  system  constructed  on  the  same  plan  as  that  of 
the  Arthropods,  with  which  the  Segmented  Worms  are 
probably  closely  related.  Others  (including  the  numerous 
parasitic  Worms)  are  not  segmented.  The  only  skeletal 
structures  possessed  by  any  Worms  are  minute  jaws,  which 
are  occasionally  preserved  as  fossils.  Otherwise,  they  are 
indicated  in  the  rocks  only  by  trails  left  on  the  mud  and 
by  remains  of  the  tubes  and  burrows  in  which  they  have 
lived.  The  whole  subkingdom  is  unimportant  to  the 
geologist. 

8.  ARTHROPODS. 

The  name  is  derived  from  the  Greek  apOpov,  joint,  and 
TTOU?,  foot,  and  refers  to  the  jointed  appendages,  or  limbs, 
which  are  so  conspicuous  in  the  Lobster  and  in  most 
Insects.  The  body  is  composed  of  a  longitudinal  series  of 
joints  or  segments,  well  shown  in  the  posterior  part  of 
a  Lobster.  The  segmented  structure  is  often  obscured 
(especially  in  the  anterior  part  of  the  body)  by  a  number 
of  the  segments  being  fused  together,  as  in  the  anterior 
part  of  a  Lobster.  Typically,  each  segment  of  the  body 
bears  a  pair  of  jointed  appendages,  which  may  be  antennae 
(or  feelers),  jaws,  accessory  mouth  organs,  legs  for  walk- 


CLASSIFICATION. 


77 


ing  or  swimming,  etc.  The  nervous  system  consists  typi- 
cally of  a  pair  of  ganglions  in  each  segment,  connected 
by  a  double  nervous  cord  along  the  ventral  side  of  the 
body,  though  in  many  cases  the  ganglions  of  several  seg- 
ments come  to  be  united. 

Four  of  the  classes  of  Arthropods  are  important  in  Ge- 
ology: —  1,  Crustaceans;  2,  Merostomes ;  3,  Arachnoids ; 
4,  Insects. 

1.  Crustaceans.  —  The  name  (from  Latin  crusta,  crust 
or  shell)  refers  to  the  fact  that  the  integument  is  gener- 
ally hardened  by  a  deposit  of  calcium  carbonate,  so  as  to 


FIGS.  112-120. 


ENTOMOSTRACANS:  Fig.  112,  Anatifa;  113,  Cythere  Americana;  114,  Sapphirina  iris,  female ; 
115,  same,  male,  x6;  116,  Calymene  Blumenbachii.  —  MALACOSTRACANS:  Fig.  117,  Por- 
cellio;  118,  Serolis,  x  £;  119,  Orchestia;  120,  Cancer. 

form  a  sort  of  shell.  The  Crustaceans  are  aquatic  Arthro- 
pods, breathing  by  means  of  gills  (or  through  the  integu- 
ment, without  special  organs  of  respiration),  and  having 
typically  the  two  anterior  pairs  of  appendages  developed 
as  antennae. 

The  Crustaceans  are  divided  into  two  subclasses,  the 
Entomostracans  and  the  Malacostracans.  In  the  former, 
the  number  of  segments  of  the  body  varies  widely,  and 
very  rarely  more  than  three  pairs  of  appendages  serve  as 
jaws  or  other  mouth  organs.  In  the  latter  subclass  the 
number  of  segments  of  the  body  never  varies  far  from  the 


78  THE   ANIMAL   AND   VEGETABLE   KINGDOMS. 

typical  number  (19)1,  and  almost  always  four  to  six  pairs 
of  appendages  function  as  mouth  organs. 

Among  the  Entomostracans,  the  Trilobites,  named  from 
Greek  rpla,  three,  and  Xo/3o?,  lobe,  in  allusion  to  the 
division  of  the  body  longitudinally  into  three  lobes,  as 
shown  in  Fig.  116,  are  an  order  now  extinct,  but  im- 
mensely abundant  in  earlier  geological  periods.  The 
Trilobites  appear  to  represent  a  very  primitive  type  of 
Crustacea,  and  they  perhaps  deserve  to  rank  as  a  distinct 
subclass.  In  the  Ostracoids  (Fig.  113),  the  integument  is 
produced  into  a  pair  of  folds,  right  and  left,  forming  a 
bivalve  carapace,  which  reminds  one  of  the  bivalve  shell  of 
a  Larnellibranch.  The  name  is  from  the  Greek  oarpaKov, 
shell.  The  Cirripeds,  or  Barnacles  (Fig.  112),  attach 
themselves  by  means  of  modified  antennae,  and  become 
covered  by  a  hard  shell  of  several  pieces,  looking  some- 
what like  the  shell  of  a  Mollusk. 

Among  the  Malacostracans  is  included  the  curious  group 
of  the  Leptostracans,  which  are  in  many  respects  inter- 
mediate between  the  typical  Malacostracans  and  the  En- 
tomostracans.  The  Leptostracans  are  now  nearly  extinct, 
though  they  seem  to  have  been  represented  in  earlier  times 
by  numerous  species,  some  of  them  being  of  large  size. 
One  of  them  is  shown  in  Fig.  233,  on  page  249.  The 
Arthrostracans,  or  Tetradecapods  (Greek  Terpa,  four,  Sexa, 
ten,  7TOU9,  foot),  have  four  pairs  of  appendages  developed 
as  mouth  organs,  and  seven  pairs  as  legs.  Here  belong 
the  Sow-bugs  and  Sand-fleas*  Three  species  are  shown 
in  Figs.  117-119.  The  highest  order  of  the  Malacostra- 
cans is  that  of  Decapods  (Greek  Se'/ca,  ten,  and  TTOI;?,  foot), 
in  whicB  six  pairs  of  appendages  are  developed  as  mouth 
organs,  and  only  five  pairs  as  legs.  Here  belong  the  Lob- 
ster and  the  Crab  (Fig.  120),  the  former  representing  the 
suborder  of  Macrurans  (Greek  yLtatf/oo?,  long,  and  ovpd,  tail), 


1  Exclusive  of  the  telson,  at  the  posterior  extremity  of  the  body,  which, 
though  it  never  bears  appendages,  is  considered  by  many  zoologists  a  true 
segment. 


CLASSIFICATION.  79 

the  latter  representing  the  suborder  of  Brachyurans  (Greek 
w,  short,  and  ovpd,  tail). 

2.  Merostomes. — The  name  is  derived  from  the  Greek 
,  thigh,  and  o-ro/ia,  mouth,  and  refers  to  the  fact  that 

some  of  the  appendages  have  their  basal  joints  developed 
as  jaws  and  their  terminal  portions  developed  as  legs. 
The  Merostomes  differ  from  the  Crustaceans  in  the  absence 
of  antennae.  The  Limulus,  or  Horseshoe  Crab,  is  the  only 
living  genus  of  this  class.  In  early  geological  times  the 
class  was  represented  by  the  Eurypterids,  one  of  which  is 
shown  in  Fig.  278,  page  271. 

3.  Arachnoids. — The  name  is  from  the  Greek  apd%vr), 
spider,  and  the  Spiders  and  Scorpions  are  typical  members 
of  the  class.     They  are  terrestrial  Arthropods,  breathing 
by  means  of  air  sacks  (lungs)  or  ramifying  air  tubes  (tra- 
cheae).   They  have  no  antennae,  two  pairs  of  mouth  organs, 
and  four  pairs  of  legs.     The  absence  of  antennae,  as  well 
as  certain  other  characters,  has  been  held  by  many  zoolo- 
gists to  indicate  a  close  relationship  to  the  Merostomes. 

4.  Insects.  —  Terrestrial     Arthropods,    breathing     by 
means  of  tracheae.     They  have  one  pair  of  antennae,  three 
pairs  of  mouth  organs,  and  (in  the  typical  subclass)  three 
pairs  of  legs.    The  Insects  are  divided  into  two  subclasses, 
—  Myriopods    and   Hexapods.      The   Myriopods    (Greek 
fjivpios,  countless,  and  TTOW,  foot)  have  numerous  legs,  the 
series  of  legs  extending  to  the  posterior  extremity  of  the 
body.     They  have  no  wings.     The  Hexapods  (Greek  ef, 
six,  and  Trow,  foot)  have  three  pairs  of  legs,  borne  on  the 
three  segments  of  the  body  (thorax)  next  behind  the  head. 
Most  of  them  have  two  pairs  of  wings ;  but  the  Flies  and 
their  allies  (Dipters)  have  only  one  pair,  and  some  Hexa- 
pods are  entirely  wingless. 

9.  TUNICATES. 

The  Tunicates  have  no  skeletons,  and  are  unknown 
in  fossil  condition.  They  appear  to  be  a  degenerate 
branch  of  the  Vertebrate  stem.  In  adapting  themselves 


80  THE   ANIMAL   AND   VEGETABLE   KINGDOMS. 

to  a  sedentary  life,  they  have  lost  most  of  the  charac- 
teristics of  Vertebrates,  though  their  relation  to  that 
group  is  indicated  by  their  embryology. 

10.  VERTEBRATES. 

The  Vertebrates,  or  vertebrated  animals,  take  their  name 
from  the  backbone,  or  vertebral  column.  The  distinctive 
character  of  the  Vertebrates  is  the  division  of  the  body 
into  a  dorsal  cavity  containing  the  central  organs  of 
the  nervous  system,  and  a  ventral  cavity  containing  the 
nutritive  viscera,  separated  from  each  other  by  an  axial 
skeleton.  In  the  lowest  Vertebrates,  as  in  the  embryos 
of  the  higher  forms,  this  axial  skeleton  appears  as  an 
unsegmented  chord  (notochord).  But,  in  all  except  the 
lowest  Vertebrates,  cartilaginous  or  bony  rings  are  devel- 
oped in  the  sheath  of  the  notochord,  which  encroach  upon 
it,  often  to  its  entire  obliteration,  forming  the  bodies  of 
the  vertebrae.  Cartilaginous  or  bony  arches  connected 
with  the  vertebral  bodies  come  to  inclose  more  or  less 
completely  the  nervous  cord  on  the  dorsal  side  of  the  axis 
and  the  viscera  on  the  ventral  side  of  the  axis.  The  axial 
skeleton  and  the  nervous  cord  both  undergo  remarkable 
modifications  at  the  anterior  extremity  of  the  body,  form- 
ing the  skull  and  brain. 

Vertebrates  are  divided  into  the  following  classes  :  —  1, 
Leptocardians ;  2,  Marsipolranchs  ;  3,  Fishes;  ^Amphibi- 
ans; 5,  Reptiles;  6,  Birds;  7,  Mammals. 

1.  Leptocardians.  —  The  name  (Greek  Xe-Trnfc,  thin,  and 
/capSia,  heart)  refers  to  the  absence  of  a  massive,  muscular 
heart,  the  blood  being  propelled  only  by  the  action  of 
muscular  tissue  diffused  through  various  parts  of  the 
arterial  system.  The  notochord  shows  itself  in  very 
primitive  condition.  There  are  no  bones,  scales,  teeth, 
limbs,  skull,  nor  brain.  Having  no  hard  parts,  these 
animals  have  never  been  preserved  as  fossils.  They  are, 
however,  profoundly  interesting,  since  they  represent, 
more  nearly  than  any  other  animals,  what  must  have  been 


CLASSIFICATION.  81 

the  primitive  type  of  Vertebrates.     The  class  is  repre- 
sented only  by  the  Amphioxus,  or  Lancelet. 

2.  Marsipobranchs.  —  The  name  (Greek  pdpo-iTros,  pouch, 
and  Ppdyxia,  gills)  refers  to  the  form  of  the  gills,  which 
are  a  series  of  pouches  on  each  side,  communicating  with 
the  pharynx.     The  Marsipobranchs  show  a  persistent  noto- 
chord,  with  no  vertebral  bodies.     They  have  no  limbs,  and 
the   mouth  is  not  provided  with  jaws.      The  Lampreys 
are   familiar   examples   of  this  class.      Their   only   hard 
parts  are  little  teeth  inserted  in  the  mucous  membrane 
of  the  mouth.     Such  teeth  might  be  preserved  as  fossils, 
but  have  not  yet  been  recognized. 

3.  Fishes.  —  These  differ  from  the  preceding  classes  in 
the  development  of  cartilaginous  or  bony  vertebral  bodies, 
and  in  the  possession  of  jaws  and  (generally)  two  pairs  of 
limbs.     They  differ  from  the  remaining  classes  in  that  the 
limbs  are  developed  as  fins,  the  respiration  is  by  gills,  and 
the  heart  consists  (except  in  one  subclass)  of  one  auricle 
and  one  ventricle.     The  teeth,  fin  spines,  scales,  and  bones 
of  Fishes  are  among  the  important  fossils  in  many  forma- 
tions. 

Fishes  are  divided  into  five  subclasses  :  —  1,  Selachians; 
2,  Placoderms ;  3,  Granoids;  4,  Teleosts ;  5,  Dipnoans. 

The  Selachians  (Greek  0-eXa^?;,  cartilaginous  fishes)  have 
skeletons  but  slightly  ossified.  The  vertebral  column 
extends  to  the  extremity  of  the  tail  fin,  generally  bending 
up  into  the  upper  lobe,  which  is  then  commonly  much 
longer  than  the  lower,  as  shown  in  Figs.  121,  123.  Such 
tails  are  called  heterocercal  (Greek  ere/oo?,  other,  and  /cep/eo?, 
tail).  In  some  Selachians,  however,  the  vertebral  column 
extends  in  a  straight  line  to  the  extremity  of  a  symmetri- 
cal tail  fin.  This  form  of  tail,  called  diphycercal,  is 
believed  to  be  the  primitive  type. 

Many  Selachians  have  strong  spines  at  the  margin  of 
some  of  the  fins  (Figs.  121-123).  They  all  have  a  skin 
roughened  by  minute  toothlike  points  (shagreen).  Some 
of  them  have  sharp  cutting  teeth,  as  shown  in  Figs.  124- 


82 


THE  ANIMAL   AND   VEGETABLE   KINGDOMS. 


126;  others  have  flat  pavement  teeth,  adapted  to  crush 
the  shells  of  Mollusks  and  Crustaceans  (Figs.  129-131). 
Figs.  127,  128,  represent  a  somewhat  intermediate  type. 
The  gills  of  Selachians  are  developed  as  a  series  of 
pouches  through  which  the  water  passes  from  the  pharynx 


FIGS.  121-131. 


SELACHIANS  :  Fig.  121,  Spinax  Blainvillii,  x  J  ;  122,  spine  of  anterior  dorsal  fin,  natural 
size ;  123,  Cestracion  Philippi,  x  £  ;  124,  tooth  of  Lamna  elegans ;  125,  Carcharodon 
angustidens ;  126,  Notidanus  primigenius ;  127,  Hybodus  minor ;  128,  Hybodus  plica- 
tilis  ;  129,  lower  jaw  of  Cestracion,  showing  pavement  teeth ;  130,  tooth  of  Acrodus 
minimus  ;  131,  Acrodus  nobilis. 

to  escape  by  holes  in  the  sides  of  the  neck.  The  arrange- 
ment resembles  that  in  the  Marsipobranchs.  In  most 
Fishes  the  gills  are  developed  as  fringes  projecting  freely 
from  the  branchial  arches  of  the  skull.  Most  of  the 
Selachians  are  commonly  known  as  Sharks  and  Rays. 
The  Placoderms  (Greek  vrXa'f,  plate,  8e^a,  skin)  have 


CLASSIFICATION.  83 

the  body,  or  at  least  its  anterior  part,  covered  with  an 
armor  of  large,  bony  plates.  Some  of  them  are  repre- 
sented in  Figs.  297-300,  on  page  285.  As  these  creatures 
are  known  only  as  fossils,  their  true  nature  is  somewhat 
doubtful.  Some  of  them  (Figs.  297,  298)  appear  to  have 
no  lower  jaw,  or  at  least  none  capable  of  preservation  in 
a  fossil  state  ;  and  it  is  doubtful  whether  they  are  truly 
Fishes.  Others  (Figs.  299,  300)  have  a  well-developed 
lower  jaw,  and  are  believed  by  many  paleontologists  to  be 
an  aberrant  group  of  Dipnoans. 

The  Ganoids  (Greek  7^1/09,  luster)  are  generally  covered 
by  hard,  lustrous,  enameled   scales,  most   commonly   of 

FIG.  132. 


GANOID  :  Palaeoniscus  Freieslebeni,  x  J. 

rhombic  form  (Figs.  132-136).  Some  Ganoids,  however, 
are  clothed  with  cycloid  scales  (Fig.  141)  like  those  of 
many  Teleosts,  from  which  they  differ  only  in  certain 
anatomical  details  relating  to  the  optic  nerves,  the  heart, 
and  the  intestine.  The  skeleton  in  the  Ganoids  varies 
greatly  in  the  degree  of  ossification,  sometimes  becoming 
as  perfectly  ossified  as  in  the  Teleosts.  The  tail  is  some- 
times heterocercal  (Fig.  132)  or  diphycercal.  In  other 
Ganoids  the  vertebral  column  stops  at  or  near  the  base 
of  the  tail  fin,  whose  lobes  then  appear  nearly  symmetri- 
cal (Fig.  133).  Such  tails  are  called  homocercal  (Greek 
6/409,  the  same,  and  /cepfcos,  tail) .  The  Ganoids  are  a  group 
now  nearly  extinct,  though  very  abundant  in  early  geo- 
logical times. 

Teleosts  (Greek  re'Xeo?,  perfect,  and  Qcrreov,  bone)  are  so 


84 


THE   ANIMAL  AND   VEGETABLE  KINGDOMS. 


named  on  account  of  the  high  degree  of  ossification  of 
their  skeletons.  With  few  exceptions,  they  are  clothed 
with  thin,  membranous  scales,  which  are  called  cycloid 
(Greek  KVK\O<;,  circle)  when  the  posterior  margin  is 
smoothly  rounded  (Fig.  141),  and  ctenoid  (Greek  terek, 
comb)  when  the  margin  is  beset  with  teeth  (Fig.  142). 
Teleosts,  with  very  few  exceptions,  have  homocercal  tails. 
The  great  mass  of  familiar  Fishes  belong  to  this  subclass. 
Dipnoans  resemble  the  Ganoids  in  many  respects,  but 
have  the  air  bladder  developed  into  a  functional  lung,  the 
auricle  of  the  heart  divided  into  two,  and  a  distinct  pul- 


138 


GANOIDS:  Fig.  133,  tail  of  Aspidorhynchus ;  134,  scales  of  Cheirolepis  Traillii,  x  12;  135, 
Palaeoniscus  lepidurus,  x  6 ;  136,  inner  surface  of  same  ;  137,  pavement  teeth  of  Gyrodus 
umbilicus ;  138,  tooth  of  Cricodus  ;  139,  Lepidosteus  osseus  ;  140,  section  of  same, 
enlarged.  —  TELEOSTS  :  141,  cycloid  scale  ;  142,  ctenoid  scale. 

monary  circulation.  In  these  characters  they  show  a 
transition  to  the  Amphibians.  They  also  differ  from 
most  Fishes,  and  agree  with  the  higher  classes  of  Verte- 
brates, in  the  mode  of  articulation  of  the  jaws  with  the 
skull.  The  name  is  from  the  Greek  S&,  twice,  and  wen, 
to  breathe,  in  allusion  to  their  possessing  both  gills  and 
lungs. 

4.  Amphibians.  —  The  name  (Greek  a/^t,  on  both  sides, 
/Sib?,  life)  refers  to  the  fact  that  most  of  these  animals  are 
partly  aquatic  and  partly  terrestrial  in  habit.  Most  .of 
them  undergo  a  strongly  marked  metamorphosis.  In 


CLASSIFICATION.  85 

their  early  stage,  they  breathe  by  means  of  gills,  have  a 
heart  with  a  single  auricle,  and  are  aquatic ;  in  adult  life, 
they  breathe  by  means  of  lungs,  have  two  auricles  and  a 
distinct  pulmonary  circulation,  and  are  more  or  less  com- 
pletely terrestrial.  Their  limbs  (rarely  wanting)  are 
developed  not  as  fins,  but  as  legs.  Toads,  Frogs,  and 
Salamanders  are  well-known  examples  of  this  class.  The 
remarkable  extinct  group  of  the  Stegocephala,  or  Laby- 
rinthodonts,  is  illustrated  on  pages  308,  352. 

5.  Reptiles.  —  These   resemble    adult   Amphibians   in 
having  a  heart  with  two  auricles  and  one  ventricle  (the 
Crocodiles   being   exceptional  among  recent   Reptiles  in 
having  the  ventricle  divided),  and  in  breathing  by  means 
of  lungs.     No  gills  are  developed  at  any  stage  of  life. 
Turtles,  Lizards,  Snakes,  and  Crocodiles  are  the  principal 
groups  of  living  Reptiles.     The  remarkable  order  Rhyn- 
chocephala  is  referred  to  and  illustrated  on  pages  308,  309. 
That  order  is  nearly  extinct,  being  represented  by  a  single 
genus  in  New  Zealand.     Numerous  orders  of  Reptiles  are 
entirely  extinct,  the  present  representatives  of  the  class 
being  only  a  remnant.     Some  of  these  fossil  groups  are 
described  on  pages  340,  352,  372. 

6.  Birds.  —  These   differ   from    Reptiles   in   having   a 
covering  of   feathers,  and  also  in  having  two  ventricles 
and  a  perfect   double    circulation.      The   more    vigorous 
circulation  and  respiration  cause  Birds  (like  Mammals)  to 
have  a  temperature  often  considerably  above  that  of  the 
surrounding  medium.     Birds  and   Mammals  are  accord- 
ingly said  to  be  warm-blooded,  while  the  preceding  classes 
are  said  to  be  cold-blooded.     The  class  of  Birds  is  at 
present  remarkably  distinct  and  homogeneous ;  but  some 
of  the  fossil  birds  (pages  356,  374)  show  characters  which 
ally  them  very  closely  with  Reptiles. 

7.  Mammals. — The  name  (from  Latin  mamma,  breast) 
refers  to  the  habit  of  suckling  the  young,  by  which  these 
animals  are  characterized. 

The  subclass  Monotremes  are  the  lowest  and  most  rep- 


8b"  THE   ANIMAL   AND   VEGETABLE   KINGDOMS. 

tilian  of  Mammals.  Like  most  Reptiles,  they  are  ovipa- 
rous ;  and  in  many  points  of  their  anatomy  they  greatly 
resemble  Reptiles.  They  are  now  represented  only  by 
the  Duckbill  (Ornithorhynchus)  and  the  Spiny  Ant-eater 
(Echidna),  both  of  which  live  in  Australasia. 

In  the  subclass  Marsupials  (Latin  marsupium,  pouch), 
the  young  are  produced  viviparously ;  but,  in  the  absence 
of  a  placenta,  the  development  is  not  far  advanced  before 
birth.  The  young  are  accordingly,  in  most  species,  carried 
by  the  mother  for  a  time  in  a  pouch  formed  by  folds  of 
skin,  within  which  the  teats  are  situated.  With  the 
exception  of  the  Opossums,  which  live  in  America,  the 
Marsupials  are  now  confined  to  Australasia,  where  they 
are  represented  by  Kangaroos,  Phalangers,  Wombats,  etc. 
Formerly  they  existed  in  all  regions  of  the  globe. 

In  the  Placentals,  or  typical  Mammals,  provision  is 
made  for  the  nutrition  of  the  embryo  before  birth,  by 
means  of  the  structure  called  the  placenta  ;  and  the  young 
are  accordingly  bom  in  a  more  advanced  stage  of  devel- 
opment. In  this  subclass  are  included  all  the  familiar 
Mammals  (with  the  exceptions  above  indicated),  as  well 
as  Man  himself. 

The  Vegetable  Kingdom. 

Plants  are  commonly  divided  into  the  two  groups, 
Cryptogams  and  Phanerogams. 

1.    CRYPTOGAMS.l 

The  name  (from  Greek  fcpvTrrds,  secret,  and  7^0?, 
marriage)  was  given  to  these  plants  by  Linnseus,  in 
allusion  to  the  fact  that  the  reproductive  organs  appeared 

1  The  group  of  Cryptogams  is  retained  simply  as  a  matter  of  conven- 
ience. It  is  a  heterogeneous  assemblage,  like  the  assemblage  of  Inverte- 
brates among  animals.  But  the  lower  plants  play  so  unimportant  a  r61e 
in  Geology,  that  it  is  not  worth  while  to  trouble  the  beginner  in  Geology 
with  the  technicalities  of  the  modern  classification. 


CLASSIFICATION.  87 

in  general  less  conspicuous  than  in  the  Phanerogams,  and 
that  in  many  of  them  the  reproductive  processes  were  in 
his  time  altogether  unknown.  Here  are  included  all 
plants  which  do  not  bear  flowers  and  produce  seeds.  The 
reproductive  bodies  are  single  cells,  and  are  called  spores. 

1.  Thallophytes.1  —  This  name  is  given  to  an  assemblage 
of  the  lower  Cryptogams,  most  of  which  agree  in  the 
negative  character  of  showing  no  definite  axis  of  upward 
growth,  and  no  distinction  of  root,  stem,  and  leaf.  They 
all  consist  entirely  of  cellular  tissue,  being  destitute  of 
wood.  These  plants  arid  the  Bryophytes  are  sometimes 
called  Cellular  Cryptogams,  in  distinction  from  the  Pteri- 
dophytes,  which  are  called  Vascular  Cryptogams.  The 
lowest  Thallophytes  are  unicellular  organisms.  Some  of 
the  higher  Thallophytes  are  large  and  complex  plants. 

Disregarding  the  differences  of  structure  of  which  a 
truly  natural  classification  must  take  note,  we  may  con- 
veniently, for  present  purposes,  divide  the  Thallophytes 
into  two  groups,  on  the  basis  of  a  single  physiological 
character.  Some  of  them  contain  chlorophyll,  and  are 
therefore  capable  of  decomposing  carbon  dioxide  and 
nourishing  themselves  upon  inorganic  materials.  These 
are  called  Algce.  Most  of  these  are  aquatic,  and  many 
of  them  are  popularly  called  Seaweeds.  Other  Thallo- 
phytes are  destitute  of  chlorophyll,  and  must  feed  on 
organic  materials.  Some  of  them  live  as  parasites  upon 
other  plants  or  upon  animals ;  others  live  upon  decaying 
organic  matters.  These  are  called  Fungi.  Mushrooms, 
Toadstools,  Molds,  Bacteria,  etc.,  are  here  included. 
The  Lichens,  which  often  appear  as  grayish  crusts  on 
rocks  and  trees  (often  mistakenly  called  Mosses),  appear 
to  be  composite  organisms,  consisting  of  an  Alga  and  a 
Fungus. 

Of  these  soft,  woodless  plants,  only  the  aquatic  Algae 
attain  any  importance  as  fossils. 

1  This  group,  like  that  of  Cryptogams,  is  heterogeneous,  and  is  here 
adopted  simply  as  a  matter  of  convenience. 


THE   ANIMAL   AND   VEGETABLE   KINGDOMS. 


FIGS.  143-148. 


DIATOMS,  highly  magnified  :  Fig.  143, 
Pinnularia  peregrina ;  144,  Pleuro- 
eigma  angulatum  ;  145,  Actinop- 
tychus  senarius ;  146,  a,  Melosira 
sulcata ;  147,  Grammatophora 
marina ;  148,  Bacillaria  paradoxa. 


Diatoms  are  unicellular  Algae  which  secrete  siliceous 
skeletons.  They  abound  in  both  salt  and  fresh  water, 
and  their  remains  often  accumulate  so  as  to  form  deposits 

of  considerable  thickness.  Sev- 
eral species  are  represented  in 
Figs.  143-148.  An  interesting 
group  of  fossil  Diatoms  is  shown 
in  Fig.  440,  on  page  392. 

Desmids  are  unicellular  Algse, 
somewhat  resembling  Diatoms, 
but  destitute  of  any  siliceous 
skeleton.  They  are  sometimes 
found  fossil  in  flint  and  chert. 

Corallines  and  Nullipores  are 
Algae  which  contain  in  their  tis- 
sues a  large  amount  of  calcium 
carbonate. 

The  Fucoids  include  many  large  species  of  Algse  whose 
fronds  have  a  leathery  consistency.  Casts  of  these  are 
found  fossil  in  many  strata. 

2.  Bryophytes.  —  The  name  is  from  Greek  fipvov,  moss, 
and  (J>VTOV,  plant.    The  plants  here  included  are  the  Liver- 
worts and  Mosses.     In  the  Mosses,  the  habit  of  growth 
resembles  that  of  the  higher  plants  in  the  development 
of  an  axis  of  upward  growth,  forming  a  leafy  stem.     The 
Bryophytes,    however,    agree   with   the    Thallophytes    in 
being  destitute  of  wood.      A  woodless  terrestrial  plant 
has  little  chance  of  preservation  in  fossil  condition,  and 
the  .Bryophytes  are  unimportant  to  the  geologist. 

3.  Pteridophytes,  or  Acrogens.  —  The  former  name  is 
from  Greek  Trrepis,  fern,  and  (pvrov,  plant;  and  the  plants 
here  included  are  the  Ferns,  Equiseta,  and  Lycopods.     In 
these  plants,  as  in  the  Phanerogams,  the  stems  are  strength- 
ened by  bundles  of  woody  fiber.      Such  plants  are  much 
less  perishable  than  the  cellular  plants,  and  accordingly 
are  much  more  important  in  Geology.     In  the  Ferns  of 
temperate  climates  the  stems  are  mostly  underground,  so 


CLASSIFICATION.  89 

, 

that  the  fronds  spring  from  the  ground  ;  but  in  some 
tropical  Tree  Ferns  the  fronds  spring  from  the  summit  of 
a  trunk  fifty  feet  or  more  in  height.  The  Equiseta  of  the 
present  time  (often  called  Horsetails,  or  Scouring  Rushes) 
are  slender  plants  with  hollow,  jointed  stems.  The 
Lycopods  are  often  called  Club  Mosses,  or  Ground  Pines. 

«A11  living  species  of  Equiseta  and  Lycopods  are  small 
plants,  rising  only  a  few  inches  above  the  ground.  In 
former  geological  times,  both  groups  were  represented  by 
large  trees. 

2.    PHANEROGAMS,  OR  PREJNOGAMS. 


Both  names  (one  from  Greek  (fravepos,  manifest,  and 
,  marriage;  the  other  from  <£atVo>,  to  appear,  and 
refer  to  the  fact  that  the  reproductive  organs  are 
conspicuous,  and  the  reproductive  processes  have  long 
been  well  known.  The  essential  reproductive  organs  are 
the  stamens  and  pistils  ;  and  these,  with  the  floral  enve- 
lopes,  which  are  generally  present  and  often  conspicuously 
colored,  constitute  the  flowers.  The  pistils  bear  the 
ovules,  which  develop  into  seeds.  A  seed  contains  an 
embryo  plant  already  formed.  In  most  Phanerogams,  as 
in  the  higher  Cryptogams,  there  is  a  definite  axis  of  up- 
ward growth,  and  a  distinct  differentiation  of  root,  stem, 
and  leaves  ;  and  in  all  Phanerogams,  as  in  the  Pterido- 
phytes,  more  or  less  of  wood  is  developed.  In  the 
arrangement  of  the  wood  cells  and  ducts  (fibrovascular 
bundles)  Phanerogams  exhibit  two  distinct  types.  In 
exogenous  stems  (Greek  ef&>,  outward,  yei>o>,  to  grow),  the 
fibrovascular  bundles  are  arranged  in  a  hollow  cylinder 
around  a  central  pith.  If  the  stem  continues  to  grow  for 
successive  years,  each  season  of  growth  adds  a  layer  of 
wood  between  the  outermost  of  the  previous  layers  and 
the  bark.  A  transverse  section  of  such  a  stem  (Fig.  149) 
shows  a  series  of  rings  corresponding  to  the  successive 
seasons  of  growth.  In  endogenous  stems  (Greek  ev&ov, 
within,  and  7eV&>),  the  fibrovascular  bundles  are  dis- 


90 


THE   ANIMAL   AND    VEGETABLE   KINGDOMS. 


FIGS.  149-152. 


tributed  through  the  stem  without  any  definite  arrange- 
ment in  concentric  zones  (see  Fig.  150). 

Phanerogams  are  divided  into  two  classes,  —  G-ymno- 
sperms  and  Angiosperms.1 

1.  Gymnosperms.  —  The    name    (from    Greek    yvfjivds, 
naked,  and  (nrepua,  seed)  refers  to  the  fact  that  the  seeds 
are  not  enveloped  in  a  closed  case,  or  ovary.     In  the  Pines 
and  other  Conifers,  the  pistil  is  simply  a  scale  upon  whose 
surface  the  ovules  are  borne.     The  dense  clusters  of  very 

simple  flowers  form  the 
so-called  cones  in  these 
plants.  The  mode  of 
growth  of  the  Gymno- 
sperms is  exogenous. 
The  wood  consists  al- 
most exclusively  of  a 
single  kind  of  cells, 
showing  under  the  mi- 
croscope peculiar  mark- 
ings (disks),  which  are 
really  pits  in  the  wall 
of  the  cell  (see  Figs. 
151,  152).  This  structure  may  be  recognized  even  in 
petrified  wood  of  Gymnosperms.  In  one  group  of  the 
Conifers, ,  the  Araucarice,  the  disks  are  arranged  alter- 
nately (Fig.  152),  arid  fossils  of  that  group  have  been 
recognized  by  that  character. 

The  two  principal  orders  of  Gymnosperms  are  the  Coni- 
fers (Pines,  Spruces,  Cedars,  etc.)  and  the  Cycads  (often 
mistakenly  called  Sago  Palms). 

2.  Angiosperms.  —  The    name    (from    Greek    ayyeiov, 
vessel,  and  oW/ofta,  seed)  refers  to  the  fact  that  the  pistil 
forms  a  closed  case,  or  ovary,  in  which  the  ovules  and 

1  In  the  Manual  of  Geology,  and  in  the  previous  editions  of  this  work, 
the  Phanerogams  are  divided  into  Exogens  and  Endogens.  Exogens  are 
equivalent  to  Gymnosperms  and  Dicotyledons,  and  Endogens  to  Mono- 
cotyledons, of  the  present  classification. 


Fig.  149,  section  of  exogenous  stem ;  150,  same  of 
endogenous;  151,  wood  cells  of  the  Conifer, 
Pinus  strobus,  showing  disks  magnified  300 
times ;  152,  same  of  Araucaria  Cunninghami. 


GEOGBAPHICAL  DISTRIBUTION   OF   MARINE   LIFE.      91 

seeds  are  developed.  The  wood  is  more  complex  in  its 
structure  than  in  the  Gymnosperms,  consisting  in  part  of 
very  slender,  thick- walled  cells  (the  ordinary  wood  cells), 
and  in  part  of  cells  of  somewhat  larger  diameter  (ducts), 
with  a  variety  of  microscopic  markings  due  to  the  thick- 
ening of  parts  of  the  cell  wall. 

The  Angiosperms  are  divided  into  two  subclasses,  — 
Monocotyledons  and  Dicotyledons. 

In  Monocotyledons,  the  embryo  in  the  seed  bears  only  a 
single  leaf  (cotyledon),  and  the  growth  is  endogenous.1 
The  leaves  are  generally  parallel-veined.  Palms,  Grasses, 
Lilies,  and  Orchids  are  examples  of  this  subclass. 

In  Dicotyledons,  the  embryo  in  the  seed  bears  a  pair  of 
opposite  leaves  (cotyledons),  and  the  growth  is  exogenous. 
The  leaves  are  generally  net-veined.  To  this  group 
belong  the  great  majority  of  the  trees  and  shrubs  of  our 
forests  and  of  the  herbs  of  our  fields  and  gardens. 


GEOGRAPHICAL  DISTRIBUTION  OF  MARINE 

LIFE. 

Range  of  Life  in  Depth.  —  Recent  investigations  have 
shown  that  living  species  not  only  inhabit  the  border 
regions  of  the  oceans,  but  also  extend  widely  and  abun- 
dantly over  a  large  part  of  the  ocean's  depths.  Fishes, 
Crabs  and  other  Crustaceans,  Worms,  Echini,  Starfishes, 
Crinoids,  Corals,  are  abundant  to  depths  of  10,000  to 
13,000  feet,  and  some  of  them  to  18,000  feet.  Crusta- 
ceans of  large  size,  allied  to  Shrimps,  many  of  them  with 
good  eyes,  have  been  found  at  all  depths  to  2900  fath- 
oms ;  and  large  Crabs,  with  perfect  eyes,  at  1700  fathoms. 
Some  species  have  a  very  wide  range  in  depth ;  one  Coral 

1  The  correlation  of  monocotyledonous  embryos  with  endogenous  stems, 
and  of  dicotyledonous  embryos  with  exogenous  stems,  holds  good  in 
general,  yet  in  some  members  of  each  group  there  are  instances  of  stems 
which  fail  more  or  less  completely  to  show  the  typical  character. 


92  THE  ANIMAL   AND   VEGETABLE  KINGDOMS. 

(a  disk-shaped  kind,  Bathyactis  symmetrica)  occurs  (states 
Moseley)  at  depths  from  30  to  2900  fathoms. 

Character  of  the  Sea  Bottom.  —  The  material  most  widely 
diffused  over  the  ocean's  bottom  is  a  fine  red  or  gray 
mud  or  clay.  But  over  vast  regions  less  than  15,000  feet 
in  depth  occurs  the  Globigerina  ooze.  At  these  and 
greater  depths  occur  areas  of  Diatom  ooze,  especially  in 
the  Antarctic  seas,  in  a  zone  between  50°  and  70°  south 
latitude ;  and  areas  of  Radiolarian  ooze,  especially  in 
tropical  and  warm-temperate  regions. 

The  character  of  the  bottom  shows  that  sediments  from 
the  rivers  of  the  continents  are  not  carried  far  out  to  sea. 
Stones  of  a  pound  weight,  and  larger,  occur  100  miles 
southeast  of  Long  Island ;  but  these  are  supposed  by 
Verrill  to  have  been  carried  out  by  shore  ice.  Clay, 
with  some  fine  quartz  sand  and  particles  of  mica,  makes 
up  the  gray  mud ;  and  the  winds  may  be  a  principal 
source  of  the  sand  and  mica.  Pumice  and  fine  materials 
of  volcanic  origin  are  also  widely  distributed,  indicating 
that  the  driftings  by  the  wind  from  volcanic  islands  have 
been  to  great  distances  and  over  very  large  areas.  The 
reddish  color  of  much  of  the  oceanic  clay  is  attributed  to 
the  oxidation  of  the  iron  in  volcanic  cinders.  Grains  and 
nodules  of  oxide  of  manganese  are  very  common  over  the 
ocean's  bottom. 

The  bottom  is  the  receiving  place  of  all  the  dead  remains 
of  the  ocean's  life,  both  plant  and  animal,  exclusive  of  the 
very  large  part  that  does  not  have  a  chance  to  reach  the 
bottom,  because  of  the  eaters.  In  the  Challenger  expe- 
dition, in  the  South  Pacific,  the  trawl  brought  up,  at  one 
haul,  more  than  1500  Sharks'  teeth  and  fragments  (not 
counting  very  small  fragments)  and  about  50  ear  bones  of 
Cetaceans.  Among  the  Sharks'  teeth  found  in  that  re- 
gion, many  are  believed  to  be  of  Eocene  age ;  and  their 
being  buried  not  more  than  a  foot,  although  lying  there 
since  the  early  Tertiary,  is  regarded  as  evidence  of  the 
very  small  amount  of  detritus  that  falls  over  the  bottom. 


GEOGRAPHICAL   DISTRIBUTION   OF   MARINE   LIFE.      93 

Causes  limiting  Distribution. — The  two  prominent  phys- 
ical causes  limiting  distribution  are  the  amount  of  (1) 
heat,  and  (2)  light. 

1.  Temperature. — The  temperature  of  the  water  varies 
(1)  with  the  zones,  from  90°  F.  in  the  tropics,  to  32°  F., 
and  even  28°  F.,  in  the  polar  seas ;  (2)  with  the  distribu- 
tion of  marine  currents,  the  warm  currents  from  the  equa- 
torial regions,  and  the  cold  from  high  latitudes ;  (3)  with 
the  depth,  the  temperature  diminishing  downward  to  35° 
F.  as  a  general  thing,  but  in  some  places  to  28°  in  the 
polar  regions  and  polar  currents.  There  is  even  in  the 
tropics  a  temperature  of  45°,  and  often  of  40°,  within  300 
fathoms  of  the  surface,  and  almost  everywhere  of  40°  or 
less,  below  1000  fathoms ;  so  that,  from  1000  fathoms  to 
the  greatest  depths,  the  variation  is  only  from  40°  to  32° 
F.,  or  in  extreme  cases  to  28°  F. 

The  influence  of  marine  currents  on  the  temperature  is 
great.  The  Gulf  Stream,  a  deep  Atlantic  current,  carries 
heat  from  the  tropical  to  the  polar  seas.  The  portion  of 
the  broad  current  which  passes  through  the  Florida  Strait 
is  as  deep  as  the  strait  (400  fathoms),  and  83°  to  44°  F. 
in  temperature,  and  has  a  maximum  velocity  of  5  miles  an 
hour.  It  washes  the  deep-water  border  of  the  Atlantic 
basin  at  depths  between  60  and  300  fathoms  off  South  Caro- 
lina, and  between  60  and  150  fathoms  (Verrill)  southeast 
of  New  England ;  crosses  the  ocean  northeastward  to  the 
British  seas,  and  has  a  temperature  of  45°  off  the  Faroe 
Islands  at  a  depth  of  600  to  800  fathoms ;  and  thence  con- 
tinues on  poleward.  From  the  polar  regions  the  waters, 
chilled  down  to  39°  to  28°  F.,  flow  back,  as  the  Labrador 
Current  along  the  east  coast  of  America,  and  also  south- 
ward beneath  the  warmer  current  over  the  ocean's  depths 
to  the  equator  and  beyond.  Comparatively  little  goes 
out  through  Bering  Strait,  because  the  depth  is  only  150 
feet. 

In  the  Pacific,  there  is  a  warm  or  tropical  current  on  the 
west  side,  answering  to  the  Gulf  Stream  of  the  Atlantic. 


94  THE   ANIMAL   AND   VEGETABLE   KINGDOMS. 

Again,  on  the  east  side  of  the  South  Pacific,  a  reverse  flow 
exists  :  a  cold-water  current  from  the  southwest  strikes  the 
submarine  slopes  of  southern  South  America,  and  carries 
cold  to  the  equator,  and  thus  narrows  the  region  of  tropi- 
cal waters. 

The  range  of  temperature  favorable  to  any  marine 
species  is  small  —  generally  not  over  20°  F.,  and  often 
less  than  15°  F.  Within  the  favorable  temperature  the 
species  thrives  ;  approaching  the  limit,  the  size  usually 
diminishes ;  and  beyond  it,  growth  and  egg-development 
cease.  A  current  too  cold  for  species  within  its  reach  is 
destructive,  even  more  so  than  one  of  too  much  warmth. 

2.  Light.  —  Light  is  the  chief  limiting  cause  as  to  depth 
(Fuchs).  If  it  were  temperature,  multitudes  of  species 
might  grow  hundreds  of  feet  below  their  present  level. 
Light  has  been  found  by  experiment  to  penetrate  down- 
ward in  the  ocean  a  little  more  than  200  fathoms ;  but 
the  light  becomes  very  feeble  long  before  this  limit  is 
reached.  The  species  of  shallow  waters  differ  to  a  large 
extent  from  the  deep-sea  species ;  they  are  (as  stated  by 
Fuchs)  the  species  of  the  light,  the  latter  the  species  of 
the  darkness.  The  two  groups  of  species,  the  ocean-border 
species  (or  those  of  the  light)  and  the  deep-sea  species  (or 
those  of  the  darkness)  are  mingled  somewhat  between 
depths  of  30  and  90  fathoms,  and  some  shore  species  ex- 
tend down  to  a  much  greater  depth. 

The  eyes  of  animals  of  the  dark  sea  depths  are  often 
rudimentary,  or  else  unusually  large.  The  blindness  is 
evidence  of  darkness ;  and  the  large  eyes,  of  adaptation 
to  the  very  feeble  light  of  the  regions.  But  this  feeble 
light  may  be,  as  Dr.  Carpenter,  Wyville  Thomson,  and 
others  have  supposed,  that  of  phosphorescence,  since 
many  Crustaceans,  Alcyoniarians,  Starfishes,  and  other 
animals  are  brightly  phosphorescent.1 

1  The  following  are  enumerated  as  the  most  characteristic  types  of  the 
dark  sea  depths  :  —  of  Corals,  Oculinidse,  Cryptohelia,  and  various  solitary 
species  ;  the  Vitreous  Sponges  ;  Crinoids  (Pentacrinus,  Rhizocrinus,  Hyo- 


GEOGRAPHICAL  DISTRIBUTION   OF   MARINE   LIFE.      95 

The  Border  Region.  —  Over  the  ocean's  border  region 
not  only  is  the  diversity  of  temperature  between  the 
equator  and  the  poles  felt  in  full  force,  but  also  that 
produced  by  the  warm  and  cold  currents.  Off  eastern 
North  America  down  to  Cape  Hatteras,  the  cold  Labrador 
current  cools  the  waters  over  the  border  region  between 
the  Gulf  Stream  and  the  shore  line ;  while  south  of  this 
cape  the  Gulf  Stream  has  possession. 

The  other  causes  limiting  distribution  in  the  border 
regions  of  the  ocean  are  :  (1)  the  condition  of  the  water, 
whether  pure,  or  impure  from  sediments  and  fresh  waters 
received  from  the  land ;  (2)  the  character  of  the  bottom, 
whether  of  mud,  sand,  or  rock,  and  whether  firm,  or  easily 
stirred  by  waves  or  currents. 

Reef-forming  Corals  grow  only  in  the  sea-border  regions 
of  tropical  seas,  and  at  shallow  depths.  They  extend  from 
the  equator  to  about  latitude  28°,  on  the  average,  where  the 
sea  temperature  of  the  coldest  month  is  not  below  68°  F. 
Owing  to  the  warm  Gulf  Stream,  they  occur  in  the  Atlan- 
tic in  32°  north  latitude,  Bermuda  being  of  coral  formation ; 
and,  owing  to  the  cold  waters  off  western  South  America, 
they  are  excluded  from  that  coast  south  of  Guayaquil.  In 
depth  the  limit  is  20  to  25  fathoms.  A  vast  variety  of 
tropical  animals  live  and  find  shelter  among  coral  reefs.  . 

Seaweeds,  like  most  other  plants,  are  species  of  the 
light ;  they  grow  mostly  within  10  fathoms  of  the  sur- 
face, and  rarely  beyond  30. 

The  Sea  Depths.  —  In  this  region,  the  range  of  tempera- 
ture is  for  the  most  part  small  —  55°  to  30°.  Only  two 
well-marked  divisions  exist :  that  of  the  cold  depths,  the 
temperature  below  45°  F.  ;  and  that  within  the  range  of 
the  tropical  currents  (as  the  Gulf  Stream  in  the  North 
Atlantic),  the  temperature  mostly  45°  to  55°  F. 

crinus,  Bathycrinus);  of  Echinoids,  Echinothurise,  Pourtalesise,  Ananchy- 
tidse  ;  of  Asterioids,  Urisinga;  Holothurians  of  suborder  Elasmopodia ;  and 
Fishes,  ribbonlike  in  form,  of  the  families  Lepidopidse,  Trachypteridse, 
Macruridse,  and  O;ihidiidse. 


96  THE   ANIMAL   AND   VEGETABLE   KINGDOMS. 

The  border  of  the  Atlantic  basin  where  swept  by  the 
Gulf  Stream  (page  93),  both  on  its  west  side  and  in  the 
British  seas,  is  crowded  with  life  —  species  of  Crustaceans, 
Echinoderms,  Polyps,  Mollusks,  Worms,  Fishes  ;  and  some 
kinds  are  larger  than  any  of  the  same  groups  found  in 
shallower  waters.  Wyville  Thomson  mentions  his  bring- 
ing up  20,000  specimens  of  one  species  of  Sea  Urchin  at 
one  haul ;  and  Verrill  and  Agassiz  state  parallel  facts  from 
the  American  seas. 

The  life  from  the  cold  and  warmer  regions  differs  to  a 
great  extent  in  species ;  but  the  more  comprehensive 
groups  represented  in  the  two  are  largely  the  same.  The 
colder  depths  are  much  less  profuse  in  life,  fail  of  some 
prominent  groups,  and  contain  many  species  of  very 
peculiar  character. 

The  cold  and  warm  currents  are  in  places  in  abrupt  con- 
tact. The  pushing  of  the  former,  along  the  eastern  sub- 
merged border  of  North  America,  over  the  narrow  warmer 
area,  in  consequence  of  a  severe  storm,  was  probably  the 
cause  of  the  destruction  of  Fishes,  Crustaceans,  etc.,  that 
took  place  during  the  winter  of  1881-82  (A.  E.  Verrill). 


PAET  III.  — DYNAMICAL  GEOLOGY. 


DYNAMICAL  GEOLOGY  treats  of  the  causes  or  origin  of 
events  in  geological  history  —  that  is,  of  the  origin  of 
rocks,  of  disturbances  of  the  earth's  strata  and  the  ac- 
companying effects,  of  valleys,  of  mountains,  of  conti- 
nents, and  of  all  changes  iii  the  earth's  features,  climates, 
and  living  species.  The  agencies  of  most  importance, 
next  to  the  universal  powers  of  Gravitation  and  Cohesive 
and  Chemical  Attraction,  are  Life,  the  Atmosphere,  Water, 
and  Heat. 

The  following  are  the  subdivisions  of  the  subject  here 
adopted: — 

1,  LIFE;  2,  THE  CHEMICAL  ACTION  OF  THE  ATMOS- 
PHERE AND  WATERS;  3,  MECHANICAL  EFFECTS  OF  THE 
ATMOSPHERE  ;  4,  MECHANICAL  EFFECTS  OF  WATER  ; 
5,  ACTION  OF  HEAT  ;  6,  MOVEMENTS  IN  THE  EARTH'S 
CRUST,  including  the  folding  and  uplifting  of  strata,  and 
the  origin  of  mountains  and  of  the  earth's  general  features. 

I.    LIFE. 

Life  has  done  much  geological  work,  by  contributing 
material  for  the  making  of  rocks.  Nearly  all  the  lime- 
stones of  the  globe,  all  the  coal,  and  some  siliceous  beds, 
besides  portions  of  rocks  of  other  kinds,  have  been  formed 
out  of  the  remains  of  living  organisms.  Both  animals  and 
plants  have  been  sources  of  the  material.  The  skeletons, 
or  stony  secretions,  of  animals,  after  fulfilling  the  pur- 

97 


98  DYNAMICAL   GEOLOGY. 

poses  of  life,  have  been  turned  over  to  the  mineral  king- 
dom, to  be  made  into  minerals  and  rocks.  Similarly, 
from  vegetable  structures  have  come  beds  of  stone,  as 
well  as  beds  of  coal.  Moreover,  fossils,  or  relics  reveal- 
ing the  form  or  structure  of  once  living  creatures,  are 
common  in  the  rocks.  This  is  the  formative  work  of  life. 
Life  has  done  geological  work  also  through  its  protective 
and  its  destructive  effects. 

1.    Formative  Work. 

Aquatic  Species  the  Principal  Rock-makers.  —  The  kinds 
of  life  which  have  contributed  most  material  to  the  earth's 
rock  formations,  and  which  are  most  common  as  fossils, 
are  the  aquatic,  and  particularly  the  marine.  This  is  so 
for  several  reasons. 

(1)  The  accumulation  of  material  for  beds  of  rock  has 
been  done  mostly  by  the  sea. 

(2)  The  species  which  have  the  most  stony  matter  in 
their    structures,   viz.,    Corals,    Crinoids,    Mollusks,    and 
Molluscoids,  are,  with  inconsiderable  exceptions,  aquatic, 
and  the  great  majority  are  marine. 

(3)  The   animal   remains    which   are    covered   by   the 
water  itself,  or  by  the  sediments  deposited  therein,  are 
protected  from  the  chemical   action  of   the  atmosphere, 
and  from  various  other  destructive  agencies.     Coal  has 
been  made  only  where  the  plants  grew  in  or  near  marshes 
or  shallow  lakes,  or  were  drifted  into  bays  or  lakes  ;  for 
the  leaves  that  fall  in  the  dry  woods  undergo  complete 
decomposition,   and  pass  away  in  gaseous  combinations. 
The  bones  of  animals  dropped  over  the  land  disappear  by 
becoming  the  food  of  other  animals,  as  well  as  by  decay. 
But  those  of  Mammals,  Birds,  and  Reptiles  living  about 
the  shores  of  lakes,  have  often  become  buried  in  lacustrine 
deposits  of  sand  or  mud,  and  thus  have  been  preserved. 
Mastodons  have  been  mired  in  marshes,  and  their  skeletons 
preserved  whole,  while  the  thousands  that  died  over  the 


LIFE.  99 

dry  land  left  no  relics.  The  wings  and  other  parts  of 
Insects  have  been  kept  perfect,  and  in  great  numbers,  in 
the  muds  of  some  ancient  ponds. 

Shells,  bones,  corals,  etc.,  after  fossilization,  have  rarely 
their  original  composition.  They  have  in  almost  all  cases 
lost  at  least  the  animal  matter  they  contained,  and  thus 
become  friable.  But  frequently  they  are  petrified ;  that 
is,  the  original  material  is  replaced  by  quartz,  calcite,  or 
(less  commonly)  pyrite,  oxide  of  iron,  an  ore  of  copper,  or 
a  silicate  of  some  kind.  Wood  is  often  thus  changed  to 
quartz,  or  to  calcite,  making  what  is  called  petrified  wood. 

Besides  water,  the  resins  that  have  exuded  from  conif- 
erous and  other  trees  have  been  good  at  catching  and 
preserving  Insects,  Spiders,  and  Myriopods  —  the  smaller 
flying  and  crawling  things  of  a  forest.  The  resin  has 
usually  undergone  a  change  to  amber  or  some  similar 
substance. 

The  preceding  review  of  the  kingdoms  of  life  brings 
out  prominently  the  fact  that  only  animals  of  rather  low 
grade  consist  largely  of  stony  secretions.  Rhizopods,  Cor- 
als, Crinoids,  Brachiopods,  and  Mollusks,  among  animals, 
and  Nullipores,  Corallines,  and  some  other  Algae,  among 
plants,  are  the  chief  workers  at  rock-making,  for  the  rea- 
son that  they  may  consist  one  half  or  more  of  stone,  and 
yet  carry  on  the  processes  of  life. 

CALCAREOUS  FORMATIONS;   LIMESTONES. 

The  method  of  forming  limestones  is,  in  general,  the 
same,  whether  the  source  of  the  calcium  carbonate  be 
shells  of  Mollusks  or  Brachiopods,  or  tubes  of  Worms, 
or  Crinoids,  or  Anthozoan  corals,  or  Hydrozoan  corals,  or 
Bryozoan  corals,  or  vegetable  corals,  as  Nullipores  and 
Corallines.  If  shells  are  in  great  profusion,  there  will 
pretty  certainly  be  also  some  of  the  various  species  of 
corals,  if  the  temperature  of  the  seas  favor;  and  over  coral 
reefs,  where  Anthozoan  corals  are  the  prominent  growth, 


100  DYNAMICAL  GEOLOGY. 

shells  of  many  species  also  abound,  with  more  or  less  of 
Millepores  and  Nullipores.  Whatever  the  species,  the 
process  is  the  same.  An  account  of  the  formation  of 
limestone  from  coral  reefs  will  therefore  serve  as  a  gen- 
eral illustration  of  the  subject. 

CORAL  REEFS  AND  ISLANDS. 

In  tropical  regions,  corals  grow  in  vast  plantations 
about  most  oceanic  islands  and  along  the  shores  of  conti- 
nents, with  a  profusion  of  other  marine  life.  In  the 
shallow  waters  the  patches  or  groves  of  coral  are  usually 
distributed  among  larger  areas  of  coral  sand,  like  small 
groves  of  trees  or  shrubbery  in  some  sandy  plains. 

The  coral  plantations  are  swept  by  the  waves,  and  with 
great  force  when  the  seas  are  driven  by  storms.  The 
corals  are  thus  frequently  broken,  and  the  fragments 
washed  about  until  they  are  either  worn  to  sand  by  the 
friction  of  piece  upon  piece,  or  become  buried  in  the  holes 
among  the  growing  corals,  or  are  washed  up  on  the  beach. 
Corals  are  not  injured  by  mere  breaking,  any  more  than 
is  vegetation  by  the  clipping  of  a  branch  ;  and  those  that 
are  not  torn  up  from  the  very  base  and  reduced  to  frag- 
ments continue  to  grow. 

The  fragments  and  sand  made  by  the  waves,  and  by 
the  same  means  strewn  over  the  bottom,  along  with  the 
shells  of  Mollusks  and  other  calcareous  relics,  are  spread 
out  in  a  bed  in  the  shallow  water  like  any  sedimentary 
material.  The  bed  consolidates  as  accumulation  goes  on, 
and  thus  becomes  a  bed  of  limestone. 

As  the  corals  continue  growing  over  this  bed,  fragments 
and  sand  are  constantly  forming,  and  the  bed  of  limestone 
thus  increases  in  thickness  until  it  reaches  the  level  of  low 
tide.  Beyond  this  it  rises  but  little,  because  corals  can- 
not grow  where  they  are  liable  to  be  left  for  hours  wholly 
out  of  water ;  and  the  waves  have  too  great  force  at  this 
level  to  allow  of  their  holding  their  places,  if  they  were 


LIFE.  101 

able  to  stand 'the  hot  and  drying  sun.  A  bed  of  lime- 
stone is  thus  produced,  which  is  the  coral  reef. 

The  coral  reef  at  or  just  above  low-tide  level  is  often 
covered  with  a  thick  growth  of  Nullipores.  Millepores 
and  Corallines  sometimes  grow  in  large  patches  among 
the  other  corals  of  the  plantation.  Occasionally,  as  has 
been  observed  at  Bermuda  and  Florida,  the  tubes  of 
Worms  (Serpulce)  furnish  important  contributions  of 
material. 

The  limestone  beds  made  from  corals  and  shells  are  not 
a  result  of  growth  alone,  as  in  the  case  of  the  deposits  formed 
from  microscopic  organisms,  but  of  growth  in  connection 
with  the  breaking  and  wearing  action  of  the  ocean's  waves 
and  currents.  Corals  and  shells,  unaided,  could  make 
only  an  open  mass  full  of  large  holes,  and  not  a  compact 
rock.  There  must  be  sand  or  fine  fragments  at  hand, 
such  as  the  waters  can  and  do  constantly  make  in  such 
regions,  in  order  to  fill  up  the  spaces  or  interstices  be- 
tween the  corals  or  shells.  If  there  is  clayey  or  ordinary 
siliceous  sand  at  hand,  this  will  suffice,  but  it  will  not 
make  a  pure  limestone  ;  in  order  to  have  the  rock  a  pure 
limestone,  the  shells  and  corals  must  be  the  source  of  the 
sand  or  fine  fragments,  for  these  alone  yield  the  needed 
calcareous  material  or  cement.  The  limestone  made  in 
this  way  by  the  help  of  the  waves  may  be,  and  often  is,  of 
impalpable  fineness  of  grain,  having  been  formed,  in  such 
a  case,  of  the  finest  coral  sand  or  mud.  In  other  cases,  it 
contains  some  imbedded  fragments  in  the  solid  bed ;  in 
others,  it  is  a  coral  conglomerate  ;  and,  over  still  other 
large  sheltered  areas,  it  is  a  mass  of  standing  corals  with 
the  interstices  filled  in  solid  with  the  sand  and  fragments. 

Along  the  shores,  above  low  tide,  the  sands  are  aggluti- 
nated into  a  beach  sand-rock,  and  the  beds  have  the  slope 
of  the  beach,  or  5°  to  15°.  The  waters  contain  calcium 
bicarbonate  in  solution ;  and,  as  the  sands,  wet  at  high 
tide,  dry  again  when  the  tide  is  out,  the  calcareous  cement 
is  deposited  between  the  grains  as  calcium  carbonate,  and 


102 


DYNAMICAL   GEOLOGY. 


so  consolidation  goes  forward.  The  cement  coats  each 
grain  with  calcium  carbonate,  and  in  this  way  the  rock 
sometimes  takes  the  character  of  an  oolite. 

The  calcareous  sands  left  dry  on  the  upper  part  of  the 
beach  may  be  blown  inland  by  the  winds,  and  piled  in 
dunes,  consolidating  into  a  wind-drift  rock,  or  seolian 
rock.  This  has  occurred  on  a  large  scale  at  Bermuda  and 
the  Bahamas  (page  121). 

FIG.  153. 


\  lew  of  a  high  island,  bordered  by  coral  reelo. 

The  coral  formations  of  the  Pacific  are  sometimes  broad 
reefs  around  hilly  or  mountainous  islands,  as  shown  in 
Fig.  153.  To  the  left,  in  the  figure,  there  is  an  inner  reef 
and  an  outer  reef,  separated  by  a  channel  of  water,  the 
inner  (/)  called  a  fringing  reef,  and  the  outer  (6)  a  barrier 
reef.  They  are  united  in  one  beneath  the  water.  At 
intervals  there  are  usually  openings  through  the  barrier 

FIG.  154. 


Coral  island,  or  atoll. 

reef,  as  at  A,  A,  which  are  entrances  to  harbors.  The 
channels  are  sometimes  deep  enough  for  ships  to  pass  from 
harbor  to  harbor.  Some  islands  are  surrounded  only  by 
a  fringing  reef,  close  to  the  shore ;  others  only  by  a  bar- 
rier reef,  separated  from  the  shore  by  a  channel  several 
miles  in  width. 

Many  coral  reefs  stand  alone  in  the  ocean,  far  from  any 
other  lands.     A  view  of  one  of  these  coral  islands,  or  atolls, 


LIFE.  103 

is  shown  in  Fig.  154,  and  a  map  in  Fig.  155.  An  atoll 
consists  of  a.  reef  encircling  a  salt-water  lake,  called  the 
lagoon.  On  the  windward  side  the  reef  first  rises  above 
the  surface,  and  becomes  covered  with  vegetation.  Very 
often,  as  in  Fig.  155,  the  leeward  part  of 
the  belt  is  dry  only  at  low  tide,  or  wooded 
only  in  spots,  so  as  to  be  a  string  of  green 
islets.  There  are  sometimes  deep  open- 
ings through  the  reef  on  the  leeward  side, 
as  at  (0)  in  Fig.  155,  so  that  ships  can 
enter  the  lagoon  and  find  good  anchorage. 
Fig.  155  is  a  map  of  one  of  the  atolls  of 
the  Gilbert  (or  Kingsmill)  Islands  in  the  APia>  of  the  Gilbert 
Pacific.  sroup'Padflc- 

The  Paumotu  Archipelago,  east-northeast  of  the  Society 
Islands,  contains  between  70  and  80  atolls ;  the  Carolines, 
with  the  Radack,  Ralick,  and  Gilbert  groups,  on  the  east 
and  southeast,  as  many  more ;  and  others  are  scattered 
over  the  intervening  ocean.  Most  of  the  high  islands 
between  the  parallels  of  28°  north  and  south  of  the  equator 
(where  the  seas  are  sufficiently  warm,  page  95)  have  a 
fringe  or  barrier  of  coral  reefs. 

The  extent  of  some  of  the  modern  reefs  matches  nearly 
that  of  the  largest  Paleozoic  reefs.  On  the  north  of  the 
Fiji  Islands  the  reef  grounds  are  5  to  15  miles  in  width. 
The  barrier  reef  of  New  Caledonia  extends  150  miles  north 
of  the  island  and  50  miles  south.  Along  northeastern 
Australia  the  reefs  extend,  although  with  many  interrup- 
tions, for  1000  miles. 

Since  the  reef-forming  corals  grow  only  where  the 
depth  is  not  more  than  about  150  feet,  the  thickness  of 
the  reef  cannot  much  exceed  that  amount,  if  the  sea 
bottom  remains  at  a  constant  level.  But  in  the  vicinity 
of  many  barrier  reefs,  and  of  atolls  in  general,  soundings 
show  a  depth  of  hundreds  or  thousands  of  feet,  apparently 
indicating  for  the  reefs  a  thickness  vastly  exceeding  the 
depth  which  is  the  limit  of  coral  growth.  Darwin  ex* 


104  DYNAMICAL  GEOLOGY. 

plained  the  facts  by  the  theory  of  a  subsidence  of  the 
ocean  bottom  in  the  region  of  these  barrier  reefs  and 
atolls.  The  author's  own  observations  upon  numerous 
coral  formations  in  the  Pacific  led  him  to  adopt  the  same 

view.     If  a  fringing  reef 
FIG-156-  had   formed  about  a  vol- 

canic island,  a  subsidence 
of  the  bottom  at  a  rate 
not  faster  than  the  rate 
of  upward  growth  of  the 

Diagram  illustrating  origin  of  atolls.  TGef,   WOllld    Certainly   COn- 

vert  the  fringing  reef  into 

a  barrier  reef,  and  (if  the  subsidence  continued  until  the 
original  island  was  submerged)  into  an  atoll.  The  theory 
is  illustrated  diagrammatically  in  Fig.  156,  the  dotted 
lines  showing  the  successive  levels  of  the  water,  and  the 
letters  F,  B,  and  A  marking  the  successive  stages  of  the 
reef, — fringing  reef,  barrier  reef,  and  atoll.1 

DEEP-SEA  CALCAREOUS  FORMATIONS. 

In  the  deep  ocean  the  Globigerina  ooze  is  limestone 
material ;  and  the  shells  of  Globigerinae  are  so  small  that 
they  do  not  need  pulverizing  for  the  making  of  a  rock. 
The  beds  contain  also  molluscan  shells  and  other  relics 
from  the  pelagic  species  of  the  ocean  and  those  of  its 

1  Darwin's  theoiy  explains  completely  the  observed  facts  with  regard 
to  coral  formation.  But  it  assumes  the  fact  of  a  great  oceanic  subsidence, 
which,  though  not  a  priori  improbable  (see  page  221),  has  not  been  inde- 
pendently proved.  Moreover,  it  has  been  shown  by  Murray,  Agassiz, 
and  others,  that,  under  certain  conditions,  both  barrier  reefs  and  atolls 
may  have  been  formed  without  subsidence.  A  coral  formation  growing 
on  a  shoal  of  small  area  would  assume  the  form  of  an  atoll  by  reason  of 
the  more  luxuriant  growth  of  corals  at  the  margin  of  the  shoal,  where 
the  water  would  be  purest.  Murray  has  suggested  that  such  a  shoal  may 
bave  been  produced  by  the  erosion  of  a  volcanic  peak  which  once  rose 
above  the  sea  level ;  and  that,  in  other  cases,  shells  of  Khizopods  and 
the  stony  secretions  of  other  forms  of  marine  life  may  have  built  up  por- 
tions of  the  sea  bottom  to  within  100  or  150  feet  of  the  surface — the 


LIFE.  105 

depths ;  and  among  them  those  of  Pteropods,  pelagic 
species,  are  common  in  some  places. 

FRESH-WATER  SHELL  LIMESTONE. 

Fresh-water  shells,  especially  those  of  the  genera  Sphce- 
rium,  LimnceuS)  Pliysa,  Planorbis,  and  Paludina,  make 
white,  often  chalky,  beds  on  the  bottoms  of  small  ponds ; 
which,  as  the  pond  shallows,  become  overlain  by  a  growth 
of  peat.  In  such  accumulations,  the  shells  are  sometimes 
but  little  broken,  and  they  then  make  shell  limestone. 
The  large  shells  of  the  Unio  group,  the  Fresh-water  Mus- 
sels of  rivers,  occasionally  make  beds,  but  seldom  of  much 
extent. 

PHOSPHATIC  FORMATIONS. 

Vertebrate  animals  have  contributed  very  little  material 
to  the  rocks,  compared  with  inferior  tribes  of  animals. 
But  they  have  been  an  important  source  of  calcium  phos- 
phate, and  the  deposits  are  often  worked,  because  the 
material  is  valuable  as  a  fertilizer.  Bones,  scales,  and 
various  tissues  of  both  Vertebrates  and  Invertebrates  con- 
tain phosphatic  material.  The  mineral  apatite,  common 
in  many  crystalline  limestones,  is  a  calcium  phosphate, 
and  is  sometimes  of  organic  origin.  Guano,  which  owes 
its  value  largely  to  its  phosphates,  has  been  made  chiefly 

depth  at  which  reef  corals  can  grow,  — and  that  only  the  upper  150  feet 
consists  of  coral  rock.  The  great  depth  of  the  lagoons  in  many  of  the 
larger  atolls  is  not  very  satisfactorily  explained  on  Murray's  theory  ;  and 
many  facts  in  regard  to  coral  formations — as,  for  instance,  the  succession 
of  small  atolls,  large  atolls,  barrier  reefs,  and  fringing  reefs,  in  passing 
outward  from  the  central  area  of  the  Pacific,  which  is  destitute  of  islands 
—  are  better  explained  on  the  theory  of  subsidence.  A  few  borings  in  a 
coral  island  to  a  depth  of  500  or  1000  feet,  with  a  drill  large  enough  to 
give  a  core  six  inches  in  diameter  for  examination,  would  settle  the  ques- 
tion as  to  whether  the  rock  below  is  of  coral-reef  origin  or  not.  The 
notion  formerly  entertained,  that  atolls  have  been  formed  upon  the 
rims  of  submarine  craters,  involves  so  many  improbabilities  that  it  has 
been  universally  abandoned. 


106  DYNAMICAL  GEOLOGY. 

from  the  excrements  of  Birds  in  dry  regions  where  the 
Birds  long  had  undisturbed  possession ;  as  on  some  small 
coral  islands  in  the  central  Pacific,  islands  off  the  Peruvian 
coast,  the  coast  of  equatorial  Africa,  and  in  the  Caribbean 
Sea.  Over  the  coast  regions  of  South  Carolina,  Georgia, 
and  Florida,  there  are  large  phosphatic  deposits  of  great 
commercial  value. 

Coprolites,  or  isolated  excrements  of  Reptiles  and  Fishes, 
and  sometimes  of  other  animals,  occur  in  many  rocks. 

The  shells  of  certain  Brachiopods  —  Lingula  and  some 
related  genera  —  are  largely  phosphatic.  These  shells 
and  the  shells  of  Crustaceans,  when  fossilized,  are  usually 
black,  because  of  the  large  amount  of  animal  matter  they 
contain,  this  portion  becoming  carbonized. 

Vegetable  tissues  also  afford  phosphates,  the  ashes  of 
ordinary  meadow  grass  affording  8  parts  of  phosphoric 
acid  in  100 ;  of  rye  straw,  4  parts ;  of  clover,  18  parts ; 
of  seaweeds,  1  to  5  parts. 

SILICEOUS  FORMATIONS. 

Siliceous  beds  of  organic  origin  are  made  chiefly  from 
the  accumulation  of  the  shells  of  Diatoms,  and,  in  the 
tropical  ocean  more  especially,  from  those  of  Kadiolarians. 
Diatom  deposits  are  common  in  marshes  beneath  the  peat 
of  the  marsh.  They  were  made  while  the  marsh  was  in 
the  state  of  a  pond.  The  deposit  looks  like  chalk,  but 
shows  under  the  microscope  that  it  consists  chiefly  of  the 
shells  of  Diatoms.  Moreover,  the  material  does  not  effer- 
vesce with  acids  like  chalk  or  limestone.  It  is  used  as  a 
polishing  powder,  also  in  making  giant  powder  or  dyna- 
mite preparations,  also  for  making  "soluble  silica." 

Some  Algae  living  in  the  geysers  of  the  Yellowstone 
Park  secrete  silica,  and  thus  make  siliceous  growths  and 
accumulations,  as  first  observed  by  W.  H.  Weed. 

Such  deposits  of  organic  silica  often  become  solidified 
by  infiltrating  waters,  and  so  converted  into  opal  or  chal- 
cedony. 


LIFE.  107 

Organic  silica  has  been  largely  distributed  through 
limestones  while  they  were  in  the  process  of  formation, 
because  Diatoms,  Sponges,  and  Radiolarians  were  living 
in  the  same  waters  that  supplied  the  shells,  corals,  and 
other  materials  of  the  limestones.  Through  the  tendency 
of  particles  of  the  same  kind  of  matter  diffused  through  a 
rock  to  collect  and  concrete  together,  being  carried  by 
percolating  waters  in  a  state  of  solution*  or  suspension,  the 
limestones  are  now  filled  with  siliceous  concretions.  The 
flint  which  constitutes  concretions  of  irregular  form  in 
some  beds  of  the  English  chalk,  and  the  chert,  or  horn- 
stone,  of  many  limestones,  have  been  thus  derived.  More- 
over, in  the  petrifaction  of  the  fossils  of  a  limestone  or 
other  rock  by  silica,  the  silica  has  often  come  from  this 
organic  source. 

CARBONACEOUS  FORMATIONS;   PEAT,  COAL,  ETC. 

The  most  abundant  contributions  from  the  vegetable 
kingdom  to  rocks  are  those  constituting  beds  of  mineral 
coal,  coal  being  made  from  woody  tissues  as  the  result  of 
a  more  advanced  stage  of  the  same  process  by  which  peat 
is  formed  (as  explained  below).  Mineral  oil  has  in  part 
the  same  source,  but  is  chiefly  of  animal  origin.  Graphite, 
which  is  pure  carbon,  is  often  also  of  vegetable  origin, 
coal  sometimes  occurring  changed  to  graphite  when  it  has 
been  subjected  to  high  heat  under  pressure.  Carbonaceous 
matter,  of  vegetable  or  animal  origin,  gives  the  black  color 
to  black  limestones  and  shales,  as  it  does  to  soils.  This  is 
proved  by  the  fact  that,  when  such  rocks  are  burnt,  they 
become  white,  owing  to  the  combustion  of  the  carbonaceous 
part. 

PEAT  FORMATIONS. 

Peat  is  an  accumulation  of  half-decomposed  vegetable 
matter  formed  in  wet  or  swampy  places.  In  temperate 
climates  it  is  due  mainly  to  the  growth  of  mosses  of  the 
genus  Sphagnum.  These  mosses  form  a  loose,  spongy 


108  DYNAMICAL   GEOLOGY. 

turf ;  and,  as  they  have  the  property  of  dying  at  the 
extremities  of  the  roots  while  increasing  above,  they  may 
gradually  form  a  bed  of  great  thickness.  The  roots  and 
leaves  of  other  plants,  or  their  branches  and  stumps,  and 
any  other  vegetation  present,  may  contribute  to  the  accumu- 
lating bed.  The  small  Crustaceans,  Worms,  and  various 
other  organisms  living  in  the  waters,  including  often  fresh- 
water Sponges,  add  to  the  material ;  the  siliceous  spicules 
of  the  Sponges  may  generally  be  found  in  the  ashes  of  the 
peat.  The  carcasses  and  excrements  of  large  animals  at 
times  become  included.  Dust  may  also  be  blown  over  the 
marsh  by  the  winds. 

In  wet  parts  of  Alpine  regions  there  are  various  flower- 
ing plants  which  grow  in  the  form  of  a  close  turf,  and  give 
rise  to  beds  of  peat,  like  the  moss.  In  Tierra  del  Fuego, 
although  not  south  of  the  parallel  of  56°,  there  are  large 
marshes  of  such  Alpine  plants,  the  cool  summers  which 
prevail  in  that  latitude  in  the  southern  hemisphere  giving 
the  vegetation  an  Alpine  character  even  at  low  altitudes. 

The  dead  and  wet  vegetable  mass  slowly  undergoes 
a  change,  becoming  an  imperfect  coal,  of  a  brownish  black 
color,  loose  in  texture,  and  often  friable,  although  com- 
monly penetrated  with  rootlets.  In  the  change  the  woody 
fiber  loses  a  part  of  its  oxygen  and  hydrogen ;  but,  unlike 
the  typical  varieties  of  coal,  it  still  contains  usually  25  to 
33  per  cent  of  oxygen.  Occasionally  it  is  nearly  a  true 
coal. 

Peat  beds  cover  large  surfaces  of  some  countries,  and 
occasionally  have  a  thickness  of  forty  feet.  One  tenth  of 
Ireland  is  covered  by  them ;  and  one  of  the  "  mosses  "  of 
the  Shannon  is  stated  to  be  fifty  miles  long  and  two  or 
three  miles  broad.  A  marsh  near  the  mouth  of  the  Loire 
is  described  by  Blavier  as  more  than  fifty  leagues  in  cir- 
cumference. Over  many  parts  of  New  England  and  other 
portions  of  North  America  there  are  extensive  beds.  The 
amount  of  peat  in  Massachusetts  alone  has  been  estimated 
to  exceed  120,000,000  cords.  Many  of  the  marshes  were 


LIFE.  109 

originally  ponds  or  shallow  lakes,  and  gradually  became 
swamps  as  the  water,  from  some  cause,  diminished  in 
depth. 

Peat  is  often  underlain  by  a  bed  of  whitish  shell  marl, 
consisting  of  fresh- water  shells  —  mostly  species  of  Lim- 
nceus,  Physa,  and  Planorbis  —  which  were  living  in  the 
lake.  Beds  of  white  chalky  material  consisting  of  the  sili- 
ceous shells  of  Diatoms,  referred  to  on  page  106,  are  often 
found  beneath  peat. 

Peat  is  used  for  fuel,  and  also  as  a  fertilizer.  Muck 
is  another  name  of  peat,  and  is  used  especially  when  the 
material  is  employed  as  a  manure ;  but  it  includes  all 
impure  varieties  not  fit  for  burning,  being  applied  to 
any  black  swamp  earth  consisting  largely  of  decomposed 
vegetable  matter. 

Peat  beds  sometimes  contain  standing  trees,  and  entire 
skeletons  of  animals  that  had  sunk  in  the  swamp.  The 
peat  waters  have  an  antiseptic  power,  and  flesh  is  some- 
times changed  by  the  burial  into  adipocere. 

2.  Protective  and  Destructive  Effects. 

Slopes  are  protected  from  erosion  by  a  covering  of  turf ; 
sand  hills,  from  the  winds,  by  tufts  of  grass  and  other 
vegetation ;  shores,  from  the  surf  in  many  places,  by  a 
growth  of  long  seaweeds  ;  and  the  outer  margins  of  coral 
reefs,  by  a  growth  of  Nullipores  over  the  exposed  surface. 

Further,  forests  keep  a  vast  amount  of  moisture  in  the 
wet  ground  beneath  them,  which  is  gradually  supplied  to 
the  streams  as  from  a  reservoir,  making  them  serviceable 
for  mills  and  other  purposes  through  the  year ;  whereas, 
if  the  forests  are  cut  away,  the  rains  fill  suddenly  the 
river  channels,  producing  disastrous  floods,  and  the  long 
droughts  which  intervene  are  seasons  of  dwindled  and 
useless  waters.  And,  besides,  the  floods  carry  away  the 
soil  from  the  steep  hillsides,  and  may  reduce  a  productive 
region  to  one  of  rocky  ledges.  These  evils  are  already  a 


110  DYNAMICAL   GEOLOGY. 

reality  in  portions  of  North  America,  and  are  on  the 
increase. 

The  common  Earthworm,  as  Darwin  has  shown  (1881), 
moves  a  great  amount  of  earth  or  soil  in  the  pellets  it 
discharges  at  the  surface.  He  found  that  the  weight 
per  acre  in  a  year  in  four  cases  was  7.56,  14.58,  16.1, 
and  18.12  tons.  Lobworms,  on  seashores,  are  even 
greater  workers,  according  to  C.  Davison,  who  reports 
that  the  amount  of  sand  carried  up  each  year  on  the  shores 
of  Holy  Island,  Northumberland,  was  equivalent  to  1911 
tons  per  acre  (1891).  Marmots  (Spermatophilus  Evers- 
mani),  in  the  Caspian  steppes,  bring  great  quantities  of 
earth  to  the  surface.  In  a  few  years  after  their  introduc- 
tion they  had  brought  up  75,000  cubic  meters  of  earth  to 
the  square  mile  (Muschketoff,  1887).  The  loosening  of 
the  soil  by  such  means  allows  it  to  be  more  easily  washed 
away  by  rains. 

Rocks,  where  jointed  or  fissured  or  laminated,  are  often 
torn  asunder  or  upturned  by  the  growth  of  a  seed  in  a 
crevice,  and  the  subsequent  enlargement  of  the  root  and 
stem  —  trunks  sometimes  growing  to  a  diameter  of  sev- 
eral feet,  and  gradually  opening  the  crevice,  and  thus  dis- 
placing great  masses.  The  same  agency  opens  crevices 
to  moisture,  and  so  promotes  decomposition ;  and  it  pre- 
pares for  the  action  of  freezing  in  winter  (page  157). 

Boring  animals  cause  destruction  in  various  ways.  The 
Mole,  Mouse,  and  some  other  animals  tunnel  embank- 
ments, and  open  channels  which  the  exit  of  the  confined 
waters  rapidly  enlarges  ;  and  sometimes  a  vast  amount  of 
erosion  is  occasioned  by  the  waters  thus  discharged.  The 
levees  of  the  Mississippi  are  thus  tunneled  by  Crawfish, 
occasioning  great  floods  and  devastations.  Boring  shells, 
as  the  Saxic&va,  weaken  the  parts  of  rocks  exposed  to  the 
surf. 

The  decay  of  vegetable  and  animal  matters  in  the  soil 
produces  organic  acids  as  well  as  carbonic  acid,  which 
corrode  rocks  and  promote  their  decomposition. 


CHEMICAL   ACTION    OF   THE    AIR    AND    WATERS.      Ill 

II.     CHEMICAL   ACTION    OF   THE   AIR   AND  ' 
WATERS. 

Geological  work  of  a  destructive  kind  is  carried  forward 
in  a  quiet  way  through  the  chemical  action  of  the  con- 
stituents of  the  earth's  atmosphere  and  waters,  preparing 
thus  for  the  rougher  mechanical  work  of  these  agents ; 
and  the  same  processes  have  their  formative  effects. 

1.  Destructive  Effects. 

Oxygen  is  a  constituent  both  of  air  and  water,  it  being 
mixed  (in  the  proportion  of  23.1  per  cent  by  weight) 
with  nitrogen  to  form  air,  and  combined  (in  the  propor- 
tion of  88.89  per  cent)  with  hydrogen  to  form  water 
(H2O).  Many  substances  in  minerals  or  rocks  have  an 
intense  affinity  for  oxygen. 

Iron  rusts  because  of  its  tendency  to  combine  with 
oxygen ;  and  iron  in  the  protoxide  state,  or  ferrous  oxide 
(FeO),  will  take  more  oxygen,  and  so  pass  to  the  sesqui- 
oxide  state,  or  ferric  oxide  (Fe2O3).  Consequently,  a 
mineral  containing  iron  in  the  former  state,  as  pyroxene, 
hornblende,  or  black  mica,  often  goes  to  destruction 
through  this  affinity ;  and  hence  rocks  containing  these 
minerals,  like  trap,  usually  suffer  easy  decomposition  ;  for 
disturbing  one  constituent  is,  like  taking  a  stone  from  an 
arch,  destruction  to  the  whole.  The  other  ingredients  of 
the  iron-bearing  mineral  are  set  free  to  make  earth,  and 
commonly  the  associated  minerals  participate  in  the  decay 
and  add  to  the  earth.  The  ferric  oxide  may  make  a  red 
earth  (red  ocher),  which  is  one  form  of  the  species  hema- 
tite. But  it  generally  combines  with  water,  and  becomes 
a  brownish  yellow  earth,  which  is  yellow  ocher,  or  the 
mineral  called  limonite.  The  hematite  or  limonite  may 
be  pure,  but  it  is  usually  mixed  with  the  other  materials 
of  the  rock,  or  makes  ocherous  stains  over  the  surfaces  of 
fissures  or  joints. 


112  DYNAMICAL  GEOLOGY. 

In  this  process  of  oxidation,  moisture  as  well  as  air 
must  be  present ;  the  oxygen  taken  up  is  usually  derived 
from  the  moisture. 

Again,  iron  when  combined  with  sulphur,  constituting 
a  sulphide  of  iron,  like  pyrite  or  marcasite  (FeS2),  or 
pyrrhotite  (FeuS12),  oxidizes  readily  (unless  in  the  firmest 
crystals),  and  passes  to  the  same  state  of  yellow  ocher, 
or  linionite.  The  sulphur  also  oxidizes,  and  becomes 
sulphuric  acid,  which  is  a  destructive  agent,  owing  to  its 
tendency  to  take  into  combination  many  of  the  ingredients 
of  minerals,  as  lime,  magnesia,  soda,  potash,  alumina,  and 
iron  oxides,  making  sulphates ;  and  it  hence  aids  much 
in  the  work  of  destruction.  This  acid  may  combine  with 
the  iron,  and  so  make  green  vitriol ;  but,  as  its  affinity  for 
the  other  substances  above  enumerated  is  stronger  than 
for  iron,  the  iron  is  usually  left  in  the  ocherous  state. 

Now  iron  sulphide,  in  the  form  of  pyrite  or  marcasite, 
is  disseminated  more  or  less  abundantly  through  nearly 
all  the  rocks  of  the  globe.  Hence,  rocks  in  all  lands  are 
undergoing  destruction  through  this  agency.  Many  a 
fair-looking  stone  is  worthless  for  building  on  account  of  it. 
It  is  the  most  universal  of  rock  destroyers.  When  the 
minute  grains  of  pyrite  in  a  granite  or  sandstone  oxidize, 
the  other  mineral  particles  of  the  rock  are  set  loose,  and 
become  discolored  with  the  ocher  that  is  made ;  and  the 
sulphuric  acid,  formed  at  the  same  time,  eats  into  some 
of  them  to  cause  their  decomposition.  Thus  the  granite 
either  (1)  disintegrates  into  a  loose  granitic  sand,  or  (2) 
becomes  decomposed  to  earth  or  clay.  Blocks  of  trap  have 
a  thin  decomposed  crust,  which  is  incessantly  receiving 
additions  inside  while  losing  outside. 

The  decomposition  of  iron  sulphide  in  shales  or  clays 
often  forms  alum,  and  makes  alum  clays,  because  of  the 
combination  of  the  sulphuric  acid  that  is  formed  with  the 
alumina  of  the  rock,  and  usually  with  some  other  element 
in  the  protoxide  state,  as  potash,  soda,  magnesia,  etc. 

When  iron  carbonate  (siderite)  is  left  exposed  to  the 


CHEMICAL  ACTION   OF   THE   AIR   AND   WATERS.     113 

air  and  moisture,  the  iron  oxidizes,  and  the  surface  color 
changes  from  grayish  white  to  brown,  yellowish,  or  black, 
owing  to  the  formation  of  limonite.  An  exposure  to  the 
weather  for  a  year  is  sufficient  to  cause  a  superficial  change; 
and  by  continued  exposure  the  whole  mass  becomes  limon- 
ite. Crystalline  limestone,  when  pure  calcite  (CaCO3) 
or  pure  dolomite  (CaMgC2O6),  is  a  durable  rock.  Col- 
umns, statues,  and  pinnacles,  as  in  the  marvelous  Milan 
cathedral,  will  stand  exposure  to  the  weather  almost  in- 
definitely. But,  if  the  limestone  contains  one  per  cent  of 
iron  combined  with  the  calcium,  the  iron  will  soon  show 
itself  over  the  exposed  surface  by  giving  it  an  iron-rust 
color,  and  the  destruction  of  structures  made  of  it  is  sure 
to  follow.  If  manganese  is  present  instead  of  the  iron,  the 
destruction  of  the  rock  is  equally  certain,  but  the  stains 
produced  are  black.  To  prevent  evil  to  marble  buildings, 
blocks  of  such  limestone  are  sometimes  smeared  with  tar 
over  all  their  surfaces,  except  those  exposed  to  view. 

Carbon  Dioxide  and  Organic  Acids.  —  Carbon  dioxide 
is  present  in  the  atmosphere,  about  3  parts  in  10,000 
consisting  of  this  gas.  It  is  present  in  all  rain  water, 
the  rain  water  deriving  it  from  the  atmosphere.  It  is 
present  in  the  soil,  being  produced  wherever  the  mate- 
rial of  plants  and  animals  is  undergoing  decomposition; 
and  thence  it  is  given  to  the  waters  percolating  through 
soils.  By  all  the  methods  mentioned,  and  also  through 
animal  respiration,  the  sea  derives  carbonic  acid.  More- 
over, in  the  earlier  ages  of  the  globe,  the  amount  of  car- 
bonic acid  in  the  atmosphere  and  waters  was  far  greater 
than  at  present.  Organic  acids  result  from  the  decompo- 
sition of  vegetable  and  animal  materials  in  the  soil ;  and, 
like  carbonic  acid,  are  carried  by  the  waters  of  the  soil 
downward  through  the  porous  rocks. 

Carbonic  acid  tends  strongly  to  form  combinations  with 
magnesia,  lime,  potash,  soda,  and  with  iron  in  the  protoxide 
state.  Hence  a  feldspar,  since  it  contains  potash,  soda,  or 
lime,  is  liable  to  have  its  alkali  carried  off  by  percolating 


114  DYNAMICAL   GEOLOGY. 

waters ;  and,  with  such  a  loss,  the  mineral  changes  to  a 
hydrous  clayey  mineral  called  kaolin  —  the  material  used 
in  making  porcelain.  Common  feldspar  yields  on  analysis 
17  per  cent  of  potash,  18.5  of  alumina,  and  64.5  of  silica ; 
and  kaolin  yields  no  potash,  14  per  cent  of  water,  40  of 
alumina,  and  46  of  silica.  Granite  and  other  rocks  are 
often  eaten  into  by  this  process,  so  as  to  be  fragile  to  the 
depth  of  a  foot  or  more,  and  sometimes  to  a  depth  of  50 
or  100  feet.  Like  results  are  produced  by  organic  acids 
in  percolating  waters. 

The  depth  of  decomposition  is  determined  by  the  depth 
to  which  moisture  is  absorbed ;  so  that  the  architectural 

value  of  a  stone  is  in- 

FIG- 157-  FlG- 158-  versely  as  its  absorb- 

ent quality.  All 
cracks  or  joints  by 
which  water  enters 
may  have  a  discol- 
ored border  (Fig. 


Decomposition  of  rocks  along  cracks.  157);     aild      the 

cess  goes  on  by  this 

means,  in  some  granite,  trap,  and  other  rocks,  until  the 
mass  becomes  reduced  to  what  looks  like  a  pile  of  large 
spheroidal  concretions  (Fig.  158)  ;  and  ends  finally  in 
making  earth,  or  loose  sand,  of  the  whole. 

The  decomposition  of  iron-bearing  minerals  is  promoted 
by  the  action  of  carbonic  acid,  or  of  organic  acids  con- 
tained in  the  soil  waters.  These  acids  extract  the  iron 
protoxide  and  make  with  it  a  soluble  salt  of  iron,  and  thus, 
by  the  aid  of  streamlets,  may  carry  the  iron  away.  The 
salt  of  iron  generally  becomes  oxidized  in  the  low  places 
or  marshes  to  which  it  may  be  carried,  and  forms  there  a 
yellow  or  brown  or  brownish  black  deposit  of  limonite  or 
a  related  ore. 

In  regions  of  dry  climate,  like  |i  large  part  of  the  Rocky 
Mountain  region,  the  waters  percolating  through  porous 
rocks,  as  sandstones,  bring  to  the  surface  of  the  rock  the 


CHEMICAL  ACTION   OF   THE   AIR   AND   WATERS.     115 

soluble  iron  compounds  produced  within  it  by  decomposi- 
tion ;  and,  by  the  deposit  of  the  iron  in  the  form  of  ferric 
oxide,  give  to  the  lofty  walls  and  bluffs  of  canons  and 
plateaus  brilliant  colors  of  buff,  yellow,  orange,  vermilion, 
and  other  shades  ;  and  often  the  tints  are  in  vertical  bands 
or  stripes,  owing  to  the  descent  of  the  solution  along  the 
vertical  surfaces.  These  colors  prevail  through  Colorado, 
Utah,  Montana,  Wyoming,  and  other  states  north  and 
south.  They  gave  the  name  of  Yellowstone  to  the  large 
lake  and  river  so  called,  and  to  the  Yellowstone  Park  in 
northwestern  Wyoming.  Were  rains  abundant,  the  iron- 
made  tints  would  be  washed  out  by  the  descending  waters, 
and  only  the  commonplace  grays  and  dull  reds  remain. 

The  organic  material  of  the  soils,  owing  to  its  using  oxy- 
gen when  decomposing,  will  take  it  from  any  Fe2O3  pres- 
ent, and  may  thus  change  it  to  FeO,  and  this  FeO  may  then 
combine  with  the  organic  acid  or  carbonic  acid  at  hand. 
Many  red  beds  of  rocks  have  lost  the  red  color  in  spots 
or  seams  or  along  cracks,  by  this  method  of  deoxidation. 

When  calcareous  grains  or  fossils  are  distributed  through 
beds  of  porous  siliceous  sandstone,  percolating  waters  will 
carry  off  the  grains  and  fossils.  But,  if  the  rocks  are  .not 
porous,  such  fossils  remain  for  indefinite  time.  Moisture 
usually  penetrates  a  compact  rock  to  a  very  small  distance 
—  generally  less  than  an  eighth  of  an  inch,  —  and  only  to 
this  depth  does  change  go  forward.  The  frequent  preser- 
vation of  calcareous  fossils,  and  the  unaltered  state  of  the 
minerals  of  much  granite  and  trap,  show  that  infiltration 
and  change  have  ordinarily  very  narrow  limits. 

Waters  containing  carbonic  acid  readily  erode  limestone. 
The  limestone  is  converted  into  calcium  bicarbonate, 
which  is  soluble.  On  exposure  to  the  air,  the  bicarbonate 
loses  its  excess  of  carbonic  acid,  and  the  limestone  taken 
up  is  again  deposited.  Thus  limestone  strata  are  eroded, 
and  caverns  made  ;  and,  by  the  depositions,  the  caverns 
are  hung  with  stalactites  and  floored  with  stalagmite. 
(See  pages  40,  144.) 


116 


DYNAMICAL   GEOLOGY. 


FIG.  159. 


2.  Formative  Effects. 

Deposits  Formed.  —  1.  By  the  decomposition  of  iron- 
bearing  limestone  or  iron  carbonate,  as  explained  in  the 
preceding  section,  great  beds  of  limonite,  of  the  purest 
quality,  have  been  made,  sometimes  over  100  feet  deep, 
and  they  often  lie  in  place  ;  that  is,  they  occupy  the  place 
of  the  rocks  from  whose  decomposition  they  were  derived. 
Those  of  Richmond  and  West  Stockbridge  in  Massachu- 
setts, of  Salisbury  in  Connecticut,  of  Millerton  and  other 
places  in  eastern  New  York,  and  of  many  localities  south 
of  New  York  in  Pennsylvania  and  Virginia  are  of 
this  kind. 

Fig.  159  represents  the  decomposition  here  described, 

as  it  is  now  going  on  at 
the  Amenia  ore  pit  in 
Dutchess  County,  east- 
ern New  York. 

Again,  the  iron  salts 
carried  for  long  periods 
to  marshes — the  pockets 
of  a  region  —  have  often 
made  large  beds  of  bog 
ore,  a  variety  of  limonite.  Such  ore  is  likely  to  contain 
sulphur  and  phosphorus  (from  the  decomposing  organic 
materials  present  in  a  marsh),  and  hence  the  iron  afforded 
is  generally  of  inferior  quality. 

2.  From  the  decomposition  of  feldspar  have  come  large 
beds   of   kaolin,    or   porcelain   clay.      Some  of   the   best 
and  largest  have  been  made  from  quartzites  containing 
disseminated  feldspar,  as  on  the  southern  margin  of  New 
Marlboro,  Massachusetts,  the  kaolin  being  removed  by  per- 
colating waters,  and  deposited  in  the  valleys  of  streams. 
Other  beds  of  kaolin  have  resulted  from  the  decomposition 
of  the  feldspar  in  granite  and  allied  rocks. 

3.  Carbonated  waters,  besides  forming  stalactites  and 
stalagmites,  have  made  large  beds  of  limestone,  like  the 


Impure  limestone,  decaying  to  limonite ;    Arnenia 
ore  pit,  New  York. 


CHEMICAL   ACTION    OF   THE   AIR   AND    WATERS.      117 

travertine  of  Tivoli,  near  Rome,  and  the  deposits  of 
Gardiners  River,  Yellowstone  Park.  Such  deposits  are 
formed  in  many  rivers  that  flow  through  limestone  coun- 
tries, and  in  lakes  into  which  such  rivers  flow. 

4.  In  dry  countries,  lakes  without  outlets  often  occur, 
the  inflow  of  water  being  balanced  by  evaporation,  so  that 
the  water  in  the  lake  is  unable  to  rise  to  a  level  at  which 
it  can  find  an  outlet.  In  such  lakes  the  soluble  materials 
present  in  river  waters  may  accumulate  to  supersatura- 
tion,  and  be  deposited.  In  regions  where  marine  sedi- 
ments are  the  prevailing  rocks,  the  soluble  ingredients 
taken  up  by  the  rivers  will  be  largely  the  same  that  exist 
in  sea  water,  as  common  salt  (sodium  chloride)  and  gypsum 
(calcium  sulphate).  In  regions  of  volcanic  rocks,  alkaline 
carbonates,  derived  from  the  decomposition  of  the  feld- 
spars and  allied  minerals,  will  be  more  abundant  than 
chlorides.  Salt  lakes  may  also  be  formed  by  the  isolation 
of  portions  of  the  sea  by  elevation  of  portions  of  the 
earth's  crust.  In  the  progressive  concentration  of  salt 
lakes,  gypsum  is  first  deposited,  being  comparatively  little 
soluble,  and  afterwards  the  salt.  Deposits  of  salt  and 
gypsum  may  be  formed  also  in  salt  marshes  and  lagoons 
along  seashores. 

Consolidation  of  Rocks.  —  Carbonated  waters,  besides 
serving  in  the  consolidation  of  limestones  (page  101), 
often  also  consolidate  sand  beds,  gravel  beds,  and  clay 
beds,  when  grains  of  limestone  are  even  sparingly  present, 
through  alternate  wetting  and  drying.  Very  commonly 
the  solidification  in  beds  of  clay  and  sand  takes  place 
around  centers  (some  grain,  or  it  may  be  fossil,  serving 
as  the.  nucleus),  making  concretions  (page  46)  in  the  bed. 
The  making  of  concretions  may  end  in  complete  consolida- 
tion. Again,  consolidation  takes  place  to  some  extent 
through  the  deposition  of  limonite  over  the  surfaces  of 
pebbles  in  gravel.  But  the  most  common  method  of 
solidifying  such  fragmental  deposits  is  through  siliceous 
waters  (page  194). 


118  DYNAMICAL   GEOLOGY. 

III.    MECHANICAL   EFFECTS   OF   THE 
ATMOSPHERE. 

The  Atmosphere  does  mechanical  work  in  denudation, 
transportation,  and  deposition  of  rock  material.  It  also 
accomplishes,  indirectly,  important  geological  work  by 
the  transportation  of  moisture.  Its  work  is  called  ^Eolian 
work,  from  the  classical  name  for  the  god  of  the  winds. 

1.    Denudation,  Transportation,  Deposition. 

The  force  of  the  wind  in  its  movements  against  objects 
varies  as  the  square  of  the  velocity.  Supposing  the  air 
to  be  of  mean  density  at  60°  F.  near  the  ocean's  level,  the 
pressure  it  exerts  on  a  square  foot  at  a  velocity  of  5  miles 
an  hour  is  equal  to  about  2  ounces  ;  at  a  velocity  of  10 
miles,  or  that  of  a  light  breeze,  8  ounces ;  of  20  miles,  a 
good  steady  breeze,  2  pounds ;  of  40  miles,  a  strong  gale, 
8  pounds;  of  60  miles,  18  pounds;  of  100  miles,  50 
pounds. 

But  the  density  diminishes  with  increasing  temperature, 
and  with  increase  of  height  above  the  sea  level.  The 
diminution  is  one  half  at  a  height  of  3|-  miles. 

Denudation.  —  The  work  of  denudation  is  carried  on 
by  the  winds,  by  (1)  the  direct  impact  of  the  air,  and 
(2)  abrasion  by  means  of  transported  sand  and  pebbles. 

Great  effects  from  impact  require  that  broad  surfaces 
of  unstable  structures  (as  the  side  of  a  house)  should  be 
exposed  to  the  moving  air,  and  the  effect  is  greater  where 
the  surfaces  struck  are  concave.  Broad  tracks  of  pros- 
trate trees  across  a  forest  are  examples  of  such  work. 
Moreover,  loose  stones  may  be  dislodged  from  natural 
walls  by  the  same  means,  besides  the  sand  and  fragments 
made  by  slow  decomposition  or  weathering  over  their 
surfaces. 

Abrasion  by  transported  material  is  another  important 


MECHANICAL   EFFECTS    OF   THE   ATMOSPHERE.       119 

means  of  denudation.  The  sands  carried  by  the  winds 
over  the  surfaces  of  rocks  sometimes  wear  them  smooth, 
or  cover  them  with  scratches  and  furrows,  as  early  observed 
by  W.  P.  Blake  on  granite  rocks  at  the  Pass  of  San  Ber- 
nardino, in  California.  The  different  minerals  in  the 
granite  were  found  to  stand  out  more  or  less  prominently 
over  the  rock,  according  to  hardness. 

In  the  more  arid  regions  of  the  Rocky  Mountains,  and 
in  deserts  elsewhere,  mountain  ledges  have  been  deeply 
worn,  and  bold  bluffs  shaped,  so  as  to  present  the  features 
usually  derived  from  denudation  by  water.  The  following 
sketch  (Fig.  160)  gives  a  good  idea  of  the  power  of  the 
winds  at  rock  sculpture,  and  affords  also  a  suggestion  as 

FIG.  160. 

' 

*  ~" 


^Eolian  denudation  in  the  Egyptian  desert. 

to  the  great  diversity  of  scenery  that  seolian  work  may 
produce.  It  represents  a  scene  in  the  Egyptian  desert. 
The  softer  layers  or  strata  are  worn  most  deeply,  and 
the  harder  left  to  cap  the  hills  and  form  cornices  and  lines 
of  molding. 

Glass  in  the  windows  of  houses  on  Cape  Cod  some- 
times has  holes  worn  through  it  by  the  same  means. 
The  hint  from  nature  has  led  to  the  use  of  sand  driven 
by  a  blast  for  cutting  and  engraving  glass,  and  even  for 
cutting  and  carving  granite  and  other  hard  rocks. 

The  transported  sands  also  rub  against  and  wear  one 
another.  This  mutual  attrition  makes  the  sand  grains 
smaller,  and  produces  also  the  finest  of  dust,  the  lightest 
of  the  wind-drift  materials. 


120 


DYNAMICAL   GEOLOGY. 


Transportation  and  Deposition.  —  The  streets  of  most 
cities,  as  well  as  the  roads  of  the  country,  often  afford 
examples  of  the  drifting  power  of  the  winds  ;  and  the 
burial  of  ancient  Rome  and  of  Egyptian  monuments  is 
among  its  effects.  The  moving  sands  of  seashores  and 
deserts  afford  the  best  opportunity  for  the  study  of  its 
methods  of  work. 

The  transporting  power  of  air  is  small  compared  with 
that  of  water,  because  of  its  lightness  and  want  of  co- 
hesion. Ordinary  stony  material,  such  as  common  sand, 
is  2100  times  heavier  than  dry  air,  while  only  2.5  to  2.7 
times  heavier  than  water.  A  strong  breeze  is  therefore 
required  to  raise  the  dust  of  a  road  for  transportation,  and 
a  still  stronger  breeze  to  raise  quartz  sand;  while  large 
pebbles  are  seldom  lifted  from  the  ground. 

The  winds,  moreover,  are  extremely  irregular  in  their 
movements  and  action.  The  trades,  over  the  ocean,  have 
a  degree  of  uniformity.  But  they  have  a  velocity  gener- 
ally of  only  10  to  20  miles  an  hour.  The  winds  that  do 
the  chief  part  of  seolian  geological  work  are  those  of 
storms,  whose  velocity  per  hour  is  from  40  to  more  than 
100  miles.  Such  winds  are  very  unsteady  in  action,  blow- 
ing in  blasts  or  gusts,  in  which  there  is  a  sudden  increase 
to  a  maximum  and  a  slower  decline  to  a  minimum.  There 
is  no  constancy  in  force  even  for  an  hour,  and  no  uni- 
formity over  large  areas. 

In  these  and  other  ways,  air  manifests  its  unsteady 
character  as  a  geological  agent,  and  contrasts  strongly 
with  water.  As  a  consequence,  the  transporting  power  of 
the  strong  winds  undergoes  rapid  variations.  The  wind 
that  carries  and  drops  pebbles,  a  few  minutes  later  carries 
only  sand  for  deposition,  and  finer  sand  follows  coarser. 

As  a  consequence,  seolian  deposits  are  generally  straticu- 
late,  finer  and  coarser  laminae  succeeding  each  other  in 
indefinite  alternations.  But  there  is  not  the  evenness  of 
layer  characterizing  aqueous  deposits,  even  when  made 
over  level  surfaces.  To  make  beds  without  straticulation 


MECHANICAL  EFFECTS   OF  THE  ATMOSPHERE.       121 

would  require  winds  without  these  irregularities,  —  little 
varying,  and  long  continuing,  —  such  as  few  regions  have, 
except  those  that  have  winds  of  too  moderate  velocity  to 
carry  any  but  the  finest  particles.  The  gusty  winds  tend, 
by  their  denuding  as  well  as  transporting  work,  to  make 
wavy  rather  than  plane  upper  surfaces.  Moreover,  any 
barrier,  as  a  projecting  rock  or  ledge,  or  a  stump,  or 
group  of  trees,  causes  a  heaping  of  the  sands  around  the 
obstacle,  and  makes  curving  surfaces  in  the  heaps,  owing 
to  the  eddies  that  are  made  in  the  air. 

On  seashores  the  loose  sands  of  the  beach  are  driven 
inland  by  the  winds,  and  thereby  often  form  parallel  ridges 
called  dunes.  They  are  grouped  somewhat  irregularly, 
owing  to  the  course  of  the  wind  among  them,  and  also  to 
little  inequalities  of  compactness,  or  to  protection  from 
vegetation.  They  form  especially  (1)  where  the  sand  is 
almost  purely  siliceous,  and  therefore  only  slightly  adhesive 
even  when  wet,  and  not  good  for  giving  root  to  grasses  ; 
and  (2)  on  windward  coasts. 

The  stratification  in  such  drift  hills  is  of  the  kind  rep- 
resented in  Fig.  161.  Successive  layers  dip  in  various 
directions,  and  are  abruptly  cat 

T  i          -          ,-,          .,!  .  FIG.  161. 

short,  showing  that  the  growing 
hill  was  often  partly  cut  down  by 
storms,  and  was  again  and  again 
completed  after  such  disasters. 

On  the  southern  shore  of  Long  Irregular  Iamination  m  drifted  sand. 
Island,  series  of  such  sand  hills, 

10  to  40  feet  high,  extend  along  for  100  miles.  They  are 
partially  anchored  by  straggling  tufts  of  grass.  The 
coast  southward  to  the  Chesapeake  is  similarly  fronted 
by  sand  hills.  They  occur  also  on  the  east  coast  of  Lake 
Michigan,  where  some  are  100  to  200  feet  in  height.  In 
Norfolk,  England,  between  Hunstanton  and  Weybourne, 
the  sand  hills  are  50  to  60  feet  high.  In  desert  regions,  the 
drifting  of  sand  takes  place  on  a  far  more  extensive  scale. 

Drift  hills  of  calcareous  sand,  from  the  disintegration  of 


122  DYNAMICAL   GEOLOGY. 

shells  and  corals,  in  Bermuda,  have  a  height  of  100  to  250 
feet.  Similar  drift  hills  occur  at  the  Bahamas.  Such 
hills  of  calcareous  sands  consolidate  through  alternations 
of  wet  and  dry,  and  thus  exhibit  well  in  sections  the 
irregular  dip  of  the  layers. 

The  drifting  of  sand  is  a  means  of  recovering  lands 
from  the  sea.  The  appearance  of  a  bank  at  the  water's 
surface  off  an  estuary  at  the  mouth  of  a  stream  is  followed 
by  the  formation  of  a  beach,  and  then  the  raising  of  hills 
of  sand  by  the  winds,  which  enlarge  till  they  sometimes 
close  up  the  estuary,  exclude  the  tides,  and  thus  aid  in  the 
recovery  of  the  land  by  the  deposition  of  river  detritus. 
Lyell  observes  that  at  Yarmouth,  England,  thousands  of 
acres  of  cultivated  land  have  thus  been  gained  from  a 
former  estuary.  In  all  such  results  the  action  of  the 
waves  in  first  forming  the  beach  is  a  very  important  part. 

Drift  sands  sometimes  overwhelm  and  destroy  forests 
and  cultivated  lands.  East  of  Lake  Michigan  the  sand 
hills  extend  to  a  height  of  100  to  200  feet  above  the  lake  ; 
and  even  215  feet  at  Grand  Haven,  where,  according  to 
A.  Winchell,  the  forest  has  been  buried  so  as  to  leave 
only  the  "  withered  tree-tops  projecting  a  few  feet  above 
the  waste  of  sands."  In  Norfolk,  England,  between 
Hunstanton  and  Weybourne,  the  sands  have  traveled 
inland  with  great  destructive  effects,  burying  farms  and 
houses.  They  reach,  however,  but  a  few  miles  from  the 
coast  line  ;  and,  were  it  not  that  the  seashore  itself  is  being 
undermined  by  the  waves,  and  is  thus  moving  landward, 
the  effects  would  soon  reach  their  limit. 

Dust  is  carried  by  storm  winds,  sometimes  hundreds  of 
miles.  Dust  from  Africa  has  fallen  on  ships  more  than 
1000  miles  from  the  coast,  and  at  points  1600  miles  apart 
in  a  north  and  south  direction  (Darwin).  Volcanic  dust 
was  carried  in  1835  from  Guatemala  to  Jamaica,  800  miles. 
In  one  dust  shower,  about  Lyons  in  France,  720,000  pounds 
of  dust  fell;  and  of  this  90,000  consisted  of  Diatoms  and 
other  organic  relics  (Ehrenberg). 


MECHANICAL   EFFECTS   OF   THE   ATMOSPHERE.       123 

2.   Winds  as  Transporters  of  Moisture. 

The  atmosphere  takes  moisture  from  the  ocean  and 
land,  proportionally  to  its  temperature,  and  transports  it. 
If  the  air  increases  in  temperature  as  it  passes  over  a 
continent,  it  keeps  taking  up  moisture,  and  so  dries  up 
the  land ;  if,  on  the  contrary,  it  loses  in  temperature,  its 
capacity  for  moisture  is  lessened,  and  it  drops  it,  making 
rain  and  mists  over  the  land.  If  the  warm  wind  strikes 
the  cold  side  or  summit  of  a  mountain,  the  moisture  is 
largely  dropped,  so  that  little  remains  for  the  region  on 
the  opposite  side  of  the  mountain,  which  therefore  experi- 
ences drought. 

The  trade  winds  are  movements  of  the  air  within  the 
tropics,  westward,  against  the  east  side  of  the  continents ; 
they  are  warm  winds,  well  charged  with  moisture.  Con- 
sequently, in  those  latitudes  the  eastern  portions  of  con- 
tinents are  regions  of  much  rain ;  and  the  farther  back 
from  the  east  coast  the  higher  mountains  are  set,  the  larger 
the  surface  benefited  by  the  rains.  The  position  of  the 
Andes,  on  the  extreme  western  margin  of  South  America, 
accordingly  gives  to  nearly  all  the  tropical  portion  of  that 
continent  an  abundant  rainfall,  making  it  the  greatest 
forest  region  of  the  globe. 

The  prevailing  winds  in  middle  latitudes,  on  the  other 
hand,  move  eastward,  being  southwest  winds  in  the  north- 
ern hemisphere,  and  northwest  winds  in  the  southern 
hemisphere.  The  great  warm- water  area  of  the  Gulf 
of  Mexico  is  thus  of  immense  service  to  eastern  North 
America,  furnishing  to  the  southwest  winds  the  abundant 
water  supply  which  makes  the  eastern  half  of  the  conti- 
nent a  region  of  moist  climate  and  abundant  forests. 

The  arid  climate  of  the  Great  Basin  and  much  of  the 
eastern  slope  of  the  Rocky  Mountains,  and  that  of  the  coast 
of  Peru  and  the  plains  of  southern  Argentina,  illustrate 
the  other  side  of  the  working  of  the  same  laws. 

Thus  the  winds  are  largely  the  distributors  of  fertility, 


124  DYNAMICAL   GEOLOGY. 

the  locators  of  great  forest  regions  and  deserts,  and  the 
limiters  of  distribution  for  the  living  species  of  the  land ; 
and  they  have  done  their  work  essentially  in  the  same  way 
through  all  past  time,  and,  in  general,  with  like  geo- 
graphical effects  over  the  same  regions  from  one  age  to 
another. 

IV.    MECHANICAL   EFFECTS   OF   WATER. 

Water  does  mechanical  work  in  the  conditions  of  — 

1.  FRESH  WATER,  or  that  of  Rivers  ; 

2.  THE  OCEAN  ; 

3.  FROZEN  WATERS,  or  Glaciers  and  Icebergs. 

1.    Fresh  Waters. 

Sources  of  Rivers.  —  The  water  of  rivers  descends  in 
the  form  of  rain  and  snow  from  the  clouds  ;  and  the  clouds 
derive  it,  by  evaporation,  from  the  surface  of  the  land, 
its  soil,  lakes,  rivers,  and  foliage,  and  more  abundantly 
from  the  ocean.  The  water  rises  in  vapor  into  the  upper 
regions  of  the  atmosphere,  and,  becoming  condensed  into 
raindrops  or  snowflakes,  falls  over  the  hills  and  plains. 
The  drops  gather  first  into  rills ;  these,  as  they  descend, 
unite  into  rivulets;  these,  again,  if  the  region  is  elevated 
or  mountainous,  into  torrents  ;  torrents,  flowing  down  the 
different  mountain  valleys,  combine  with  other  torrents 
to  form  rivers  ;  and  rivers  from  one  mountain  chain  some- 
times join  the  rivers  from  another,  and  make  a  common 
stream  of  great  magnitude  and  great  drainage  area,  like 
the  Mississippi  or  the  Amazon. 

The  Mississippi  has  its  tributaries  among  all  the  eastern 
heights  of  the  great  Rocky  Mountain  chain,  throughout 
a  distance  of  1000  miles,  or  between  the  parallels  of  35°  N. 
and  50°  N. ;  and  another  set  of  tributaries  gather  waters 
from  the  Appalachian  chain,  between  western  New  York 
and  Alabama.  Rills,  rivulets,  torrents,  and  rivers  com- 


MECHANICAL  EFFECTS   OF   WATER.  125 

bine,  over  an  area  of  1,244,000  square  miles,  to  make 
the  great  central  southward-flowing  stream  of  the  North 
American  continent. 

The  amount  of  water  poured  each  year  into  the  ocean  by 
the  Mississippi  averages  19£  trillions  (19,500,000,000,000) 
of  cubic  feet,  varying  from  11  trillions  in  dry  years  to  27 
trillions  in  wet  years.  This  amount  is  about  25  per  cent 
of  that  furnished  by  the  rains,  the  rest  being  lost  mostly 
by  evaporation.  The  pitch  of  the  river  from  Memphis 
down  its  last  885  miles  is  4.82  inches  per  mile  at  low 
water. 

The  Amazon  extends  its  arms  north  of  the  equator  to 
the  parallel  of  3°,  and  south  to  that  of  20°,  and  has  a 
drainage  area  of  2,500,000  square  miles,  equal  to  a  third 
of  all  South  America.  Starting  within  sixty  miles  of  the 
Pacific,  it  flows  as  a  mountain  torrent  through  the  gorges 
of  the  eastern  range  of  the  Andes,  and  then  the  navigable 
part  of  the  river  commences,  the  length  of  which  to  the 
Atlantic  is  over  3300  miles.  It  discharges  into  the  ocean 
five  times  as  much  water  as  the  Mississippi,  because  of 
the  large  precipitation  (50  inches)  over  much  of  the  area. 
For  3000  miles,  the  mean  pitch  of  the  stream  is  less  than 
an  inch  a  mile,  the  descent  in  this  distance  being  only 
210  feet. 

Snowy  mountains  deal  out  water  gradually,  under  the 
control  of  the  sun  and  winds,  day  and  night  and  summer 
and  winter  making  alternations  in  the  supply  to  the 
streams.  Forest  regions,  also,  are  like  reservoirs  in  hold- 
ing long,  and  yielding  up  gradually,  the  waters  supplied 
to  them.  Lakes  are  literally  reservoirs,  storing  water  for 
slow  discharge. 

THE  MECHANICAL  WORK  OF  RIVERS. 

Working  Power.  —  The  working  power  of  a  river 
depends  primarily  on  (1)  the  volume  of  flowing  water, 
and  (2)  the  amount  of  fall  in  the  descent  to  sea  level,  01 
to  the  final  outlet.  According  to  the  mathematical  law 


126  DYNAMICAL   GEOLOGY. 

respecting  falling  bodies,  the  energy  should  vary  as  the 
product  of  volume  and  height  of  fall.  This  working 
power  is  expended  in  friction,  between  the  water  and  the 
bed  of  the  water  way,  between  the  water  and  the  atmos- 
phere, and  between  the  molecules  of  the  water  itself; 
and  in  transportation  of  rock  material  (which  must  mean- 
while be  supported  in  opposition  to  gravitation).  In 
these  ways,  the  energy  of  a  stream  is  generally  so  far 
used  up  that  it  has  very  little  velocity  as  it  approaches 
its  outlet. 

Kinds  of  Work. — The  kinds  of  work  done  by  streams 
are  the  following  :  — 

1.  Transportation  of  earth  and  stones,  and  often  also 
of  logs  and  leaves,  for  deposition  down  stream. 

2.  Excavation  of  a  waterway,  by  the  impact  of  the  mov- 
ing water,  and  by  that  of  the  transported  stones  and  earth. 

3.  Mutual    abrasion    of    the    transported    stones    and 
earthy  particles,  reducing   them   in   size,  and   rendering 
them  thereby  easier  to  transport. 

The  action  of  running  waters  in  wearing  down  the 
elevated  portions  of  the  earth's  surface  toward  sea  level 
is  called  denudation,  or  degradation. 

Nearly  all  valleys  of  the  world  owe  their  formation 
in  large  degree  to  excavation  by  running  water.  Even 
valleys  which  had  their  origin  in  differential  elevation 
of  the  earth's  crust,  have  been  considerably  modified  by 
river  erosion. 

DENUDATION. 

Causes  and  Conditions  influencing  Denudation.  —  Denu- 
dation is  carried  on  chiefly  by  the  process  of  abrasion. 
Direct  blows  of  the  water  are  efficient  in  rapid,  plung- 
ing streams,  especially  where  the  rocks  are  much  jointed, 
fissile,  or  fragile,  and  .where  cavities  or  recesses  exist 
to  receive  the  blows ;  but  over  firm  rocks  of  flat  or 
convex  surface  they  have  little  effect.  Blows  of  solid 
material,  as  grains  of  sand  or  stones,  are  more  effective 


MECHANICAL   EFFECTS   OF   WATER.  127 

than  those  of  water.  Hence,  up  to  a  certain  limit,  abra- 
sion is  increased  by  the  load  of  sediment  which  the  stream 
is  carrying.  '  Beyond  that  limit,  however,  the  load  of  sedi- 
ment so  far  diminishes  the  velocity  of  the  stream  as  to 
diminish  or  entirely  abolish  its  power  of  erosion. 

Moreover,  the  decomposing  and  dissolving  action  of 
water  and  other  agencies  gives  important  aid  in  the  work 
of  denudation.  Decomposition  and  disintegration  (pages 
111-115)  are  going  on  over  almost  all  exposed  surfaces  of 
rocks,  thus  making  softened  material  for  the  abrading  and 
transporting  rills  and  rivers.  Solution  also  has  consid- 
erable effect,  especially  in  limestone  regions;  it  helps 
much  in  the  excavation  of  valleys,  and  finds  in  the  joints 
of  the  rocks  a  chance  to  begin  the  work  (page  144). 

The  rounded  stones,  gravel,  and  earth  of  fields,  and 
also  the  material  of  most  geological  formations,  have  been 
made  to  a  large  degree  by  the  wearing  action  of  waters 
—  either  those  of  streams  over  the  land,  or  those  of  the 
ocean.  But  this  action  is,  and  ever  has  been,  greatly 
aided  by  the  processes  of  decomposition  and  disaggrega- 
tion  due  to  the  elements  —  causes  that  are  sufficient  alone 
to  turn  angular  blocks  of  most  rocks  into  rounded  masses. 

Rivers  do  the  chief  part  of  their  work  in  times  of  floods. 
Many  a  torrent  is  a  quiet  brook  at  other  seasons,  or  per- 
haps only  a  string  of  pools.  At  low  water  the  pitch  of 
the  stream,  or  that  of  its  upper  surf  ace,*  is  at  its  minimum, 
while  the  ratio  of  friction  to  the  amount  of  water  is  at  a 
maximum,  so  that  the  water  often  lies  almost  still  between 
its  banks.  But  at  flood  height  the  pitch  is  increased,  and 
the  friction  relatively  decreased ;  and  hence  comes  the  flood 
velocity.  The  Connecticut,  from  Hartford  to  the  Sound, 
36  miles  (in  an  air  line),  is  a  tidal  stream,  zero  in  working 
force,  at  low  tide  and  low  water ;  but,  in  its  highest  flood 
(30  feet  at  Hartford),  it  has  a  mean  pitch  of  10  inches  a 
mile,  and  flows  off  with  great  rapidity.  On  mountain 
streams  the  transition  is  often  from  almost  or  quite  zero 
to  a  succession  of  cataracts  of  vast  working  force. 


128 


DYNAMICAL   GEOLOGY. 


FIG.  162. 


Rain  prints. 


Work  of  Denudation.  —  Denudation  commences  with  the 
raindrop;  for  a  shower  of  rain  consists  of  an  infinitude 
of  little  waterfalls,  each  having  power  to  denude  by  strip- 
ping off  grains  from  the  surface  of  soft  or  weathered  rocks, 
and  to  excavate  where  it  falls  on  a 
mud  flat  or  sand  flat  recently  laid 
bare  (as  by  the  ebb  of  the  tide),  and 
make  the  raindrop  impression.  The 
quick  succession  of  drops  ordinarily 
obliterates  the  special  work  of  each; 
but,  in  a  shower  of  large  drops  and 
short  duration,  they  remain,  so  that 
rain  prints  (Fig.  162)  are  not  un- 
common markings  on  the  surface  of 
strata. 

The    next  sweep    of    the   waters 
over  the  surface  may  fill   the  cavi- 
ties with  fine  mud  or  sand,  and  so 
they  may  become  buried  records. 

A  wind  may  give  the  drops  greater  efficiency  in  abra- 
sion. At  the  same  time  it  may  register  its  direction  in 
the  elliptical  form  of  the  rain  prints. 

When  the  drops  strike  a  gravel  bed,  stones  in  the  gravel 
may  protect  the  material  directly  be- 
neath, while  the  surrounding  material 
is  eroded.  Thus  slender  columns  are 
left,  each  capped  with  a  pebble  or 
bowlder. 

Fig.  163  shows  a  miniature  exam- 
ple of  this  phenomenon.  It  was  ob- 
served by  the  author  in  1887,  near  the 
path  which  leads  down  to  the  bottom  of 
the  crater  of  Kilauea,  on  the  Island  of  Hawaii.  The  drops 
had  fallen  from  shrubbery,  wet  by  the  heavy  mist  con- 
densed from  the  steam  of  the  volcano.  In  other  localities, 
columns  scores  of  feet  in  height  have  been  carved  by  rain- 
drops in  glacial  drift  and  similar  materials. 


FIG.  163. 


Drop-made  columns,  natu- 
ral size. 


MECHANICAL  EFFECTS   OF   WATER. 


129 


The  raindrops  make  rills  and  rivulets  ;  and  these,  as 
they  hurry  on  their  way,  carry  off  light  earth  or  sand, 
and  so  make  channels  and  deepen  their  beds.  This  may 
be  well  seen  along  many  a  roadside,  or  over  sand  banks 
during  and  after  a  shower. 

Torrents,  from  combined  rivulets,  work  with  greater 
power,  tearing  up  rocks  and  trees  as  they  plunge  along, 


FIG.  164. 


Eastern  part  of  the  Island  of  Maui,  Hawaiian  Islands. 

and,  in  the  course  of  time,  making  deep  gorges  or  valleys 
in  the  mountain  slopes ;  and  rivers,  when  in  full  action, 
work  with  vast  power,  making  wide  valleys  over  the 
breadth  of  the  continent.  The  slopes  of  a  lofty  mountain, 
exposed  through  ages  to  the  action  described,  finally 
become  reduced  to  a  series  of  valleys  and  ridges,  with 
towering  peaks  and  crested  heights  —  all  these  effects 
originating  in  the  fall  of  raindrops  or  snowflakes. 


130 


DYNAMICAL   GEOLOGY. 


The  successive  steps  in  the  degradation  of  mountains 
are  well  illustrated  among  the  volcanic  cones  of  the 
Pacific.  The  surface  of  such  mountains  is  kept  free  from 
river  channeling  as  long  as  the  volcano  is  active,  because 
of  the  successive  outflows  of  lava.  This  is  illustrated  in 


FIG.  165. 


Northwest  peninsula  of  Tahiti,  the  coral  reefs  excluded  (the  lower  side  is  the  northern). 

Mauna  Loa,  on  the  Island  of  Hawaii  (see  map,  Fig.  198, 
page  179).  Denudation  has  its  chance  only  after  the  vol- 
canic activity  has  begun  to  decline.  The  waters  of  the 
rains  (which  are  always  most  copious  about  the  summits 
of  high  mountains),  beginning  in  rivulets  down  the  slopes, 


MECHANICAL   EFFECTS   OF   WATEB.  131 

first  gather  sufficient  strength  for  effective  denudation  to- 
ward the  base  of  the  mountain. 

In  the  eastern  volcanic  cone  of  Maui  (see  map,  Fig.  164), 
the  process  of  valley-making  has  commenced.  The  chan- 
nels of  the  rivers  of  the  north  side,  as  the  map  indicates, 
extend  only  halfway  up  the  mountain;  on  the  northeast, 
or  the  most  rainy  side,  they  extend  up  to  a  level  just  be- 
low the  summit ;  while  on  the  west  side,  they  are  merely 
narrow  trenches,  and  are  dry  through  nearly  all  the  year. 
The  last  eruption  of  the  volcano  took  place,  according  to 
tradition,  about  250  years  since. 

Fig.  165  represents  the  topography  of  the  northwest 
peninsula  of  Tahiti,  one  of  the  Society  Islands.  The 
volcano  has  been  long  extinct  —  long  enough  for  the 
extension  of  the  river  channels  to  the  summit,  and  for 
the  continued  excavation  of  these  channels  until  they 
have  become  valleys  1000  to  3000  feet  deep,  with  spacious 
amphitheaters,  or  cirques,  at  their  head,  reducing  the  island 
to  a  group  of  knife-edge  ridges  and  steep-sided  gorges. 
The  highest  peaks  (a  and  b  on  the  map)  are  parts  of  the 
narrow  ridges  thinned  down  to  a  breadth  at  top  of  one  to 
ten  feet,  while  8000  and  7000  feet  in  altitude.  They  face 
with  a  nearly  vertical  front,  at  one  point  at  least  4000  feet 
high,  two  of  the  grandest  of  the  amphitheaters.  The 
amphitheaters,  or  cirques,  are  made  by  water  alone,  in  a 
tropical  region,  and  show  that  the  help  of  glaciers  is  not 
required,  as  sometimes  supposed,  for  such  results. 

Forms  of  Valleys ;  Channels  and  Flood  Grounds  of  Riv- 
ers. —  The  valleys  excavated  by  mountain  streams  have 
a  V-shaped  cross  section.  But,  when  the  river  flows  into 
a  region  of  gentle  declivities  or  plains,  the  waters  lose 
in  velocity,  and  may  even  deposit  sediment  over  the  bed, 
instead  of  deepening  it  by  excavation.  At  the  same  time, 
the  waters,  no  longer  able  to  deepen  their  channel,  begin 
to  erode  laterally,  undermining  their  banks,  and  making  a 
flood  plain,  over  which  the  waters  spread  in  their  annual 
or  occasional  freshets. 


DYNAMICAL   GEOLOGY. 


Nearly  all  streams  over  the  plains  and  lower  slopes  of 
the  land  have  narrow  channels  for  dry  times,  and  flood 
grounds  which  they  cover  in  times  of  great  rains  or  melt- 
ing snows.  The  alluvial  plains  of  rivers  are,  in  part,  these 
plains  formed  by  lateral  erosion,  but  covered  by  deposits 
left  by  the  flooded  stream ;  in  part,  areas  reclaimed  from 
sea  or  lake,  as  in  the  formation  of  deltas  (pages  138-140). 


Marble  Caflon,  Colorado  River. 

Cascades.  —  Cascades  are  often  formed  where,  in  the 
course  of  a  rapid  stream,  there  are  alternations  of  hard  and 
soft  rocks.  The  hard  rocks  resist  wear,  while  the  soft  ones 
easily  yield ;  and  thus  a  plunge  begins,  which  increases  in 
force  as  it  increases  in  extent.  Rills  and  rivulets  made  by 
a  shower  of  rain  along  roadsides  or  sand  banks  often  illus- 
trate this  feature  of  great  mountain  streams. 


MECHANICAL   EFFECTS   OF   WATER.  133 

Canons. — When  a  region  has  been  recently  elevated  to 
a  high  altitude,  giving  the  streams  power  for  rapid  erosion, 
especially  if  the  rocks  are  nearly  horizontal,  the  valleys  cut 
by  the  rivers  have  usually  bold  rocky  sides.  In  many 
parts  of  the  Rocky  Mountains,  the  streams  have  worked 
their  way  down  through  the  rocks  for  hundreds,  and  in 
some  places  even  thousands,  of  feet.  Such  a  valley  is 
called  a  canon. 

These  canons  have  great  depth  and  magnitude  on  the 
Colorado  River,  over  the  west  slope  of  the  Rocky  Moun- 
tains, between  longitude  111°  W.  and  115°  W.  For  more 
than  300  miles  there  is  a  nearly  continuous  canon,  3000 
to  6000  feet  deep.  The  preceding  sketch,  from  one  of 
the  excellent  photographs  of  the  region  by  the  artist  of 
Powell's  Expedition,  represents  a  portion  of  it,  called  the 
Marble  Canon.  The  rocks  stand  in  nearly  vertical  preci- 
pices on  either  side  of  the  stream,  and  the  height  above 
the  water  to  the  top  of  the  bluff  seen  in  the  distance  is 
5000  feet.  The  deep  gorge  is  the  result  of  erosion  by  the 
stream. 

Fig.  167  presents  a  view  of  another  part  of  the  canon, 
and  shows  better  the  details  of  the  stratification  in  its 
lofty  walls. 

In  many  places,  the  wall  of  the  canon  is  carved  into 
alcoves  and  buttresses  in  infinite  variety.  Some  of  the 
larger  projecting  masses  imitate  on  a  colossal  scale  the 
forms  of  oriental  temples.  All  these  picturesque  features 
are  the  work  of  the  sculpturing  waters  since  the  time 
of  the  early  Tertiary.  Moreover,  over  the  country  to  the 
northward,  rise  plateaus  and  mountains,  in  which  the 
strata  are  piled  up  to  an  additional  altitude  of  5000  to 
7000  feet,  and  these  are  portions  of  great  formations  that 
once  spread  across  the  whole  region. 

Sculpture  of  Mountain  Forms ;  Mountains  of  Circum- 
denudation .  —  Given  a  great  elevated  plateau  in  a  region 
of  rains,  and  mountain  sculpturing  will  go  on  about  it, 
continue  until  all  is  ridge  and  valley,  not  a  square 


134 


DYNAMICAL    GEOLOGY. 


mile  of  the  original  plateau  retaining  its  flat  surface ;  and 
the  resulting  crested  ridges  may  rise  thousands  of  feet 
above  the  bottoms  of  the  valleys,  if  the  plateau  was  one 
of  sufficient  height.  The  Catskill  Mountains,  New  York, 
are  an  example  of  mountains  of  circumdenudation. 


FIG.  16T. 


Wall  of  Colorado  Caflon. 


The  following  figures,  by  Lesley,  illustrate  some  of  the 
results  of  sculpturing  by  water,  in  both  horizontal  and 
upturned  or  flexed  strata.  In  the  production  of  such 
erosion  forms,  the  ocean  has  sometimes  taken  part  during 
the  submergence  of  a  continent ;  but  the  final  results  are, 
in  almost  all  cases,  due  to  the  chiselings  of  fresh  waters. 
The  figures  here  given  are  small,  but  the  elevations  they 


MECHANICAL   EFFECTS   OF   WATER. 


135 


represent,  as  illustrated  in  the  Appalachians,  Jura,  and 
many  other  mountain  regions,  are  often  thousands  of  feet 
in  height. 

When  the  beds  are  horizontal,  or  nearly  so,  but  of  unequal 
hardness,  the  softer  strata  are  easily  worn  away,  and  by 
this  means  the  harder  strata  become  undermined.  Table- 


FIG.  168. 


Fm.  169. 


Erosion  forms  in  nearly  horizontal  strata. 

shaped  mountains  are  often  thus  formed,  having  a  top  of 
the  harder  rock,  and  the  declivities  banded  with  projecting 
shelves  and  intervening  slopes.  Figs.  168,  169  represent 
the  common  character  of  such  hills.  Such  flat-topped 
elevations  in  the  Colorado  region  have  been  called  mesas, 
from  the  Spanish  for  table. 

When  the  beds  are  inclined  between  5°  and  30°,  there 
is  a  tendency  to  make  hills  with  a  long  back  slope  and 
bold  front;  but,  with  a  much  larger  dip,  the  ridges  are 
more  nearly  symmetrical. 

When  the  dipping  strata  are  of  unequal  hardness,  and 


170 


FIGS.  1TO-175. 


173 


Erosion  forms  in  synclinal  strata. 

lie  in  folds,  there  is  a  wide  diversity  in  the  results  on  the 
features  of  the  landscape. 

Figs.  170-175  represent  the  effects  from  the  erosion 
of  a  synclinal  region  consisting  of  alternations  of  hard 
and  soft  rocks.  The  protection  of  the  softer  beds  by 
the  harder  is  well  shown. 


136  DYNAMICAL   GEOLOGY. 

Anticlinal  strata  give  rise  to  another  series  of  forms, 
in  part  the  reverse  of  the  preceding,  and  equally  varied. 
Figs.  176-179  represent  some  of  the  simpler  cases.  When 
the  back  of  an  anticlinal  mountain  is  divided  (as  in  Figs. 
176-178),  the  mountain  apparently  loses  the  anticlinal 


FIGS.  176-179. 


Erosion  forms  in  anticlinal  strata. 

character,  and  the  parts  are,  in  aspect,  simply  monoclinal 
ridges.  In  Fig.  179  the  anticlinal  character  is  distinct  in 
the  central  portion,  while  lost  in  the  parts  on  either  side. 
In  Fig.  179,  to  the  right,  the  protection  afforded  to  softer 
strata  by  even  a  vertical  stratum  of  hard  rock  is  illus- 
trated :  the  vertical  stratum  forms  the  axis  of  a  low 
ridge. 

TRANSPORTATION  AND  DEPOSITION. 

Fact  of  Transportation.  —  It  has  been  stated  that  the 
massive  mountains  have  been  eroded  into  ridges  and  val- 
leys by  running  water.  The  material  worn  out  has  been 
transported  somewhere  by  the  same  waters. 

Part  of  the  transported  material  in  all  such  operations 
goes  to  form  the  great  alluvial  plains  that  occupy  the 
river  valleys,  especially  in  the  lower  part  of  their  course. 
Part  is  carried  to  the  sea  into  which  the  river  empties, 
where  it  meets  the  counteracting  waves  and  currents,  and 
is  distributed  for  the  most  part  along  the  shores,  filling 
estuaries  or  bays,  or  making  deltas,  and  extending  the 
bounds  of  the  lands  ;  or  to  lakes,  with  or  without  outlets. 

The  mountains  of  a  continent  are  ever  on  the  move 
seaward,  and  thus  contribute  to  the  enlargement  of  the 
seashore  plains.  The  continent  is  losing  annually  in  mean 
height,  but  gaining  in  width,  or  extent  of  dry  land. 


MECHANICAL  EFFECTS   OF   WATER.  137 

Transporting  Power  of  Water.  —  The  transporting  power 
of  running  water  is  very  great  when  the  flow  is  rapid. 
Large  stones  and  masses  of  rock  are  torn  up  and  moved 
onward  by  the  mountain  torrent.  A  current  of  four 
miles  an  hour  will  carry  stones  2  J  inches  in  diameter ; 
of  two  miles,  pebbles  of  0.6  inch ;  of  two  thirds  of  a  mile, 
fine  sand,  about  .064  inch  in  diameter;  of  one  third  of  a 
mile,  fine  earth  or  clay,  the  particles  .016  inch  in  diame- 
ter ;  the  mean  diameter  of  the  largest  transportable  parti- 
cles varying  as  the  square  of  the  velocity,  supposing  them 
of  like  density. 

Hence,  as  a  stream  loses  in  velocity,  it  leaves  behind 
the  coarser  material,  and  carries  only  the  finer;  if  the 
rate  becomes  very  slow,  it  drops  the  gravel  or  the  sand, 
and  bears  on  only  the  finest  earth  or  clay.  Consequently, 
where  the  current  is  swift,  the  bottom  (if  not  consisting 
of  rocky  ledges)  is  stony  or  pebbly  ;  and  where  the  water 
is  still,  or  nearly  so,  the  bottom  is  muddy.  Slow  rivers 
and  small  lakes  have  commonly  muddy  borders. 

Amount  of  Material  Transported. — The  amount  of  trans- 
ported material  varies  with  the  size  and  current  of  the 
rivers  and  the  kind  of  country  they  flow  through.  The 
Mississippi  carries  annually  to  the  Gulf  of  Mexico,  accord- 
ing to  Humphreys  and  Abbot,  on  an  average,  812,500,- 
000,000  pounds  of  silt  —  equal  to  a  mass  one  square  mile 
in  area  and  241  feet  deep,  —  and  its  bottom  waters  push 
on  enough  more  to  make  the  241  feet  268  feet.  The  proc- 
ess slowly  lowers  the  drainage  area  of  the  river,  and  the 
mean  amount  of  lowering  indicated  by  the  facts  stated  is 
one  foot  in  4920  years.  The  total  annual  discharge  of 
silt  by  the  Ganges  has  been  estimated  at  6,368,000,000 
cubic  feet. 

Besides  the  silt,  rivers  carry  what  the  waters  take  into 
solution.  The  amount  is  generally  between  a  third  and 
a  half  of  that  mechanically  transported  ;  but  sometimes 
nearly  an  equal  weight.  If  one  half,  in  the  case  of  the 
Mississippi,  the  period  of  4920  years  would  be  reduced  to 


138  DYNAMICAL   GEOLOGY. 

3280.  The  salts  held  in  solution  are  often  about  one  half 
calcium  carbonate,  and  the  rest  calcium  sulphate,  sodium 
chloride  (common  salt),  sodium  carbonate,  and  inagnesian 
and  potash  salts,  with  traces  of  silica  and  other  ingredi- 
ents. In  some  cases  the  rivers  carry  the  salts  to  inland 
seas  or  lakes,  which  have  no  drainage  toward  the  ocean, 
and  which  therefore  are  saline  (page  117).  Moreover,  arid 
plains  become  saline  because  of  the  capillary  action  which 
brings  moisture  from  below  to  the  surface,  as  evaporation 
goes  on  above,  depositing  the  contained  saline  ingredients, 
such  as  the  sodium  chloride,  sodium  carbonate,  and  mag- 
nesian  salts  of  such  places. 

Alluvial  or  Fluvial  Formations.  —  The  deposits  made 
by  the  transported  material,  which  now  constitute  the 
alluvial  plains  of  the  river  valleys,  cover  a  large  part  of 
a  continent,  since  rivers  or  smaller  streams  are  almost 
everywhere  at  work.  They  are  made  up  of  layers  of 
pebbles  or  gravel,  and  of  earth,  silt,  or  clay,  especially 
of  these  finer  materials.  Logs,  leaves,  shells,  and  bones 
occur  in  them  :  but  these  are  rare ;  for  whatever  floats 
down  stream  is  widely  scattered  by  the  waters,  and  to  a 
great  extent  destroyed  by  wear  and  decay.  The  level  of 
the  alluvial  plain  is  ordinarily  about  that  of  the  level  of 
the  higher  floods.  The  spreading  waters,  by  here  losing 
their  velocity,  owing  to  friction,  build  up  the  deposits. 
The  river  margin  is  often  a  little  above  flood  level,  owing 
to  the  shrubbery  growing  along  it,  and  to  the  abundant 
deposit  of  sediment  where  the  water  flowing  outward  from 
the  channel  onto  the  flood  plain,  receives  the  first  check  to 
its  velocity. 

Terraces.  —  River  valley  or  fluvial  formations  often 
have  the  form  of  terraces.  Terraces  are  in  general  rem- 
nants of  old  flood  plains,  the  rivers  having  deepened 
their  channels  on  account  of  elevation  of  the  land ;  and 
seashore  flats  and  beaches,  and  horizontal  lines  of  wave 
erosion  on  cliffs,  have  often  been  left  high  in  the  same 
movements. 


MECHANICAL   EFFECTS   OF   WATER. 


139 


Estuary  and  Delta  Formations. —  The  detritus  discharged 
by  the  river  at  its  mouth  tends  to  fill  up  the  bay  into 
which  it  empties,  and  make  wide  flats  on  its  borders,  and 
thus  contract  it  to  the  breadth  merely  of  the  river  current. 


Where  the  tides  are  feeble  and  the  river  large,  the  de- 
posits about  the  mouth  of  the  stream  gradually  encroach 
on  the  ocean,  and  make  great  plains  and  marshy  flats, 
which  are  intersected  by  the  many  mouths  of  the  river 


140  DYNAMICAL   GEOLOGY. 

and  a  network  of  cross  channels.  Such  a  formation  is 
called  a  delta.  Fig.  180  represents  the  delta  of  the 
Mississippi,  the  white  lines  being  the  water  channels,  and 
the  black  areas  the  great  alluvial  plains.  The  delta  prop- 
erly commences  below  the  mouth  of  Red  River,  where  the 
Atchafalaya  Bayou,  or  side  channel  of  the  river,  begins. 
The  whole  area  is  about  12,300  square  miles ;  about  one 
third  is  a  sea  marsh,  only  two  thirds  lying  above  the  level 
of  the  gulf. 

The  deltas  of  the  Nile  and  the  Ganges  are  similar  in 
general  features  to  the  delta  of  the  Mississippi. 

The  detritus  poured  into  the  ocean  where  the  tides  or 
currents  are  strong,  and  a  considerable  part  of  that  where 
the  tides  are  feeble,  goes  to  form  seashore  flats  and  sand 
banks  and  offshore  deposits.  In  their  formation  the 
ocean  takes  part  through  its  waves  and  currents,  and  hence 
they  are  more  conveniently  described  in  connection  with 
the  remarks  on  the  work  of  the  ocean. 

HISTORY  OF  RIVERS. 

Youth  and  Old  Age  of  Rivers.  —  The  work  of  excava- 
tion tends  toward  the  lowering  of  the  bed  of  a  stream  to 
the  sea  level.  The  process  involves  the  wearing  away  of 
waterfalls  and  rapids  ;  the  draining  of  the  lakes  along 
the  river  course,  as  far  as  these  have  their  beds  above  sea 
level  ;  and  the  filling  up  of  lake  basins,  even  those  that 
descend  below  that  level.  Reducing  the  slope  of  the  bed 
deprives  the  waters  of  working  power,  and  finally  the 
stage  is  reached  when  abrasion  and  deposition  over  the 
bed  balance  each  other.  Thus  rivers  pass  from  youth  to 
old  age. 

The  condition  of  balance  between  erosion  and  deposi- 
tion has  been  called  by  Powell  the  condition  of  base  level; 
and  he  has  formulated  the  important  general  law  that  a 
river  always  works  toward  its  base  level,  eroding  its  bed 
when  it  is  too  high,  and  filling  it  up  when  it  is  too  low. 


MECHANICAL    EFFECTS    OF   WATER.  141 

When  the  river  ends  in  a  lake  without  outlet,  the 
process  terminates  at  the  lake,  but  is  otherwise  the  same 
as  above  described. 

The  history  of  a  river  is  often  modified  by  continental 
changes  of  level.  An  elevation  may  rejuvenate  streams 
that  are  approaching  old  age,  or  a  subsidence  may  bring 
the  streams  to  a  premature  old  age. 

In  a  region  which  has  undergone  subsidence,  the  lower 
part  of  a  river's  course  may  be  below  base  level.  In  that 
case,  deposition  will  be  in  excess,  and  the  level  of  the  bed 
will  be  annually  raised.  Consequently,  during  floods,  the 
waters  along  the  region  of  the  shallowed  channel  will 
spread  more  and  more  widely,  as  the  years  pass,  over  the 
country  either  side,  with  disastrous  encroachments  on 
forests  and  whatever  is  in  their  way.  Man,  to  protect  his 
buildings  and  cultivated  fields,  raises  the  banks,  or  builds 
dikes  or  levees  along  them ;  but  the  waters  cannot  be 
crowded,  and  at  intervals  they  sweep  away  the  confining 
levees,  to  the  confusion  of  the  dwellers  on  the  "  recovered  " 
lands. 

Again,  the  extraordinary  floods  of  a  Glacial  period  have 
given  temporary  increase  of  vigor  to  enfeebled  rivers. 

Moreover,  changes  of  level  have  sometimes  joined  the 
head  of  one  stream  to  the  trunk  of  another;  or  made 
a  northward-flowing  stream  of  one  that  had  previously 
flowed  southward ;  or  converted  a  region  of  once  active 
rivers  into  a  vast  lake.  Rivers  were  few  and  small  when 
lands  were  small ;  and  multiplied  and  extended  and  finally 
became  combined  into  great  drainage  systems,  with  the 
growth  and  completion  of  the  continents. 

The  effect  of  the  long  work  of  the  waters  over  the  land 
is  the  gradual  degradation  of  the  hills  and  mountains, 
reducing  great  regions  to  approximately  level  plains  — 
peneplains  (from  the  Latin  pene,  almost,  and  planum, 
plain),  as  they  have  been  called  by  W.  M.  Davis;  and 
finally,  in  theory  at  least,  the  reduction  of  the  whole 
continent  to  the  condition  of  a  base-level  plain. 


142  DYNAMICAL  GEOLOGY. 

Cause  of  Direction  of  Flow.  —  The  simple  explanation  of 
the  direction  of  flow  in  a  river  is  that  it  was  determined 
by  the  slope  of  the  land.  But  in  many  cases  the  course  is 
due  not  to  the  present  slopes  and  conditions,  but  to  others 
that  existed  at  some  earlier  time.  The  working  waters 
have  sometimes  started  on  their  way  to  the  sea,  Avhen  the 
topography  was  very  different  from  the  present ;  and  they 
have  kept  their  old  course  in  spite  of  such  obstacles  as 
folds  or  faults  developed  transversely  to  their  course. 
Such  drainage  has  been  called  by  Powell  antecedent 
drainage ;  and  that  which  is  a  consequence  of  existing 
conditions,  consequent  drainage.  When  a  stream  has  cut 
through  the  entire  thickness  of  the  formation  upon  which 
it  commenced,  and  is  flowing  now  in  unconformably  un- 
derlying rocks,  without  regard  to  their  structure,  the 
drainage  is  said  to  be  superimposed. 

SUBTERRANEAN  WATERS. 

Origin  and  Course  of  Subterranean  Waters.  —  A  part 
of  the  water  that  falls  on  the  earth's  surface  —  on  its 
mountains  as  well  as  its  plains  —  sinks  through  the  ground 
and  into  the  rocks  beneath,  wherever  there  are  openings 
or  crevices,  or  looseness  of  texture,  and  thus  becomes 
subterranean.  The  waters  usually  pass  easily  through 
sandstones ;  but  over  a  clayey  or  other  compact  stratum 
they  accumulate,  and  often  make  wet,  springy  soil  above  ; 
or,  if  the  stratum  is  inclined,  they  may  descend  to  great 
depths,  or  come  to  light  again  wherever  it  outcrops  at  a 
lower  level.  The  descending  waters  sometimes  gather 
into  subterranean  streams,  which  have  powers  of  abrasion. 
Over  large  areas  in  some  limestone  regions,  and  in  many 
volcanic  regions,  surface  streams  are  wanting,  because  of 
the  cavernous  recesses ;  the  waters  carry  on  an  under- 
ground system  of  drainage.  Thus  come  springs,  subter- 
ranean streams  large  and  small,  and  copious  outflows 
beneath  the  sea  level  along  coasts. 


MECHANICAL  EFFECTS  OP  WATER. 


143 


A  region  of  horizontal  limestone  abounds  in  sink-holes, 
as  well  as  caverns  ;  and  sometimes  rivers  plunge  down 
the  openings  into  the  recesses  below,  and  are  lost,  or 
emerge  again  in  fuller  flow  a  mile  or  more  away. 


FIG.  181. 


MAP  OF  THE 
MAMMOTH  CAVE 

From  "The  Mammoth  Cave  Illustrated" 
ByH.C.HOVEY  AND  R.E.CALL 

SCALE  OF  FEET 

2000 


144  DYNAMICAL   GEOLOGY. 

Ordinary  waters  easily  erode  limestone,  because  they 
contain  carbonic  acid  (page  115).  Through  the  joints  or 
fissures  the  waters  find  a  way  downward,  and  the  erosion 
they  produce  widens  the  joints,  often  forming  funnel- 
shaped  sink-holes.  At  the  bottom  of  the  sink-hole  the 
waters  work  laterally,  eroding  channels  and  chambers,  in 
long  series  and  varying  directions ;  and  if,  later,  they 
succeed  in  penetrating  to  a  still  lower  level,  another  tier 
of  chambers  is  begun.  Undermining  also  goes  on,  causing 
falls  of  rock,  which  are  sometimes  large  enough  to  make 
feeble  earthquakes.  Occasionally  some  part  of  the  roof 
caves  in,  and  the  cavern,  with  the  river  inclosed,  becomes 
open  to  the  light,  and  thus  affords  an  example  of  one 
method  of  making  limestone  gorges. 

The  preceding  map  (modified  from  Hovey's  "  Celebrated 
American  Caverns,"  with  additions  by  R.  E.  Call)  shows 
the  passages  and  chambers  of  Mammoth  Cave,  Kentucky. 
This  cave  occupies  an  area  of  several  square  miles  in  the 
Subcarboniferous  limestone.  The  length  of  the  caverns 
in  this  limestone  in  Kentucky  (a  rock  200  to  1000  feet 
thick)  is  estimated  by  Professor  Shaler  at  100,000  miles. 
Luray  Cavern,  in  Luray  Valley,  Virginia,  is  comparatively 
small;  but,  as  described  by  Mr.  Hovey,  it  is  one  of  the  most 
remarkable  in  the  world,  for  the  beauty  of  its  stalactitic 
hangings  and  the  grandeur  of  its  subterranean  chambers. 

In  many  caverns,  bones  of  the  animals  that  have  in- 
habited them,  including  sometimes  those  of  Man,  with  his 
implements  of  stone  or  shell  or  other  material,  are  found 
buried  beneath  or  within  the  stalagmite  that  covers  the 
floor  —  the  perpetual  dripping  keeping  up  its  constant 
deposition  (pages  40,  115). 

Caves  exist  in  the  elevated  coral  reefs  of  the  Pacific, 
which  are  certainly  of  comparatively  recent  origin.  One, 
on  the  island  of  Atiu,  near  Tahiti,  has  "interminable 
windings"  and  many  chambers,  "with  fretwork  ceilings 
of  stalactite"  (J.  Williams).  There  are  others  on  Oahu, 
which  give  a  passage  to  streams. 


MECHANICAL   EFFECTS    OF    WATER. 


145 


The  erosion  may  be  helped  forward  (1)  by  the  oxida- 
tion of  pyrite  (page  112)  where  it  is  present,  the  result- 
ing sulphuric  acid  turning  limestone  into  gypsum ;  and 
also  (2)  by  the  formation  of  nitric  acid  (probably  from 
the  nitrogen  of  the  air,  by  means  of  micro-organisms), 
which  corrodes  the  limestone,  making  calcium  nitrate. 
The  caves  of  Kentucky  and  Indiana  have  afforded  a  large 
amount  of  this  nitrate  for  the  making  of  niter. 

Subterranean  waters  often  become  mineral  waters. 
They  are  made  calcareous  by  limestones  along  their  course; 
saline,  by  the  saline  ingredients  of  rocks ;  sulphurous,  by 
decomposing  iron  sulphides ;  carbonated,  by  any  acid,  as 
sulphuric,  attacking  a  limestone  and  setting  carbonic  acid 
free ;  chalybeate,  by  the  reduction  of  ferric  oxide  in  pres- 
ence of  organic  matters,  and  the  formation  of  ferrous 
bicarbonate  ;  magnesian,  by  the  decomposition  of  minerals 
containing  magnesium.  They  may  become  warm  waters 
through  subterranean  heat,  and  may  receive  vapors  and 
various  mineral  materials  from  the  depths  below. 

Artesian  Wells.  —  When  strata  are  inclined,  and  water 
descends  along  one  of  the  layers  between  others  that  are 
sufficiently  impervious  to  confine  it,  the  pressure  increases 
with  the  depth ;  so  that  the  water  will  rise  through  a  bor- 
ing made  down  to  it, 
and  sometimes  in  a 
high  jet.  The  princi- 
ple is  illustrated  in 
Fig.  182,  in  which  ab 
is  the  water-bearing 
stratum,  be  the  boring, 
and  eb  the  amount  of 
descent.  The  height  of 
the  jet  falls  much  short  of  be,  chiefly  on  account  of  the 
underground  friction. 

Such  wells  are  called  Artesian  wells  or  borings,  from  the 
district  of  Artois  in  France,  where  they  were  early  made. 
The  Artesian  well  of  Grenelle  in  Paris  is  1798  feet  deep, 


Fir,.  182. 


Section  illustrating  Artesian  wells. 


146  DYNAMICAL  GEOLOGY. 

and  when  it  was  first  made  the  water  darted  out  to  a 
height  of  112  feet.  One  at  St.  Louis  has  a  depth  of  3843  J 
feet,  but  without  getting  water,  because  the  region  for 
many  miles  around  is  one  of  horizontal  rocks.  A  boring  at 
Wheeling,  West  Virginia,  has  been  carried  to  the  depth  of 
4500  feet  without  finding  water.  A  well  at  Schladenbach 
near  Leipzig  is  5736  feet  in  depth.  Such  wells  are  made 
for  agricultural  and  manufacturing  purposes  in  many  dry 
regions,  and  they  have  proved  successful  even  in  Sahara. 
Landslides.  —  Landslides  are  of  different  kinds:  — 

1.  The  sliding  of  the  surface  earth,  or  gravel,  of  a  hill 
down  to  the  plain  below.     This  effect  may  be  caused  by 
the  waters  of  a  severe  storm  wetting  the  material  deeply 
and  giving  it  greatly  increased  weight,  besides  loosening 
its  attachment  to  the  more  solid  mass  below. 

2.  The  sliding  down  a  declivity  to  the  plain  below  of 
the  upper  layer  of  a  rock  formation.     This  may  happen 
when  this  upper  layer  rests  on  a  clayey  or  sandy  layer, 
and  the  latter  becomes  very  wet  and  greatly  softened  by  the 
waters ;   the  upper  layer  slides  down  on  the  softened  bed. 

3.  The  settling  of  the  ground  over  a  large  area.     This 
may  take  place  when  a  layer  of  clay  or  loose  sand  becomes 
wet  and  softened  by  percolating  waters,  and  then  is  pressed 
out  laterally  by  the  weight  of  the  superincumbent  layers. 
But  such  a  result  is  not  possible  unless  there  is  a  chance 
for  the  wet  layer  to  move  or  escape  laterally.     Sometimes 
part  of  a  wet  clayey  layer,  pressed  to  one  side  in  this  way, 
is  left  very  much  folded,  while  the  associated  sandy  layers 
have  their  usual  regular  bedding. 

2.  The  Ocean. 

The  ocean  is  vast  in  extent  and  vast  in  the  power  which 
it  may  exert.  But  its  mechanical  work  in  Geology  is 
mostly  confined  to  its  coasts  and  to  soundings,  where  alone 
material  exists  in  quantity  within  reach  of  the  waves  or 
currents. 


MECHANICAL   EFFECTS   OF   WATER. 


147 


The  saltness  of  the  ocean  gives  it  a  density  of  1.0240  to 
1.0278,  that  of  pure  fresh  water  being  1.  It  is  slightly 
the  greatest  in  the  tropics,  because  of  the  evaporation. 
A  cubic  foot  weighs  about  64  pounds.  There  are  three 
consequences  of  the  saltness:  —  (1)  slightly  greater  trans- 
porting power  than  fresh  water,  on  account  of  its  density  ; 
(2)  much  quicker  deposition  of  the  finest  sediment,  the  salt 
causing  a  flocculation  and  rapid  precipitation  of  minute 
clayey  particles,  which  in  pure  water  remain  in  suspension 
for  an  indefinite  period  ;  (3)  a  supply  of  common  salt  and 
magnesian  salts,  etc.,  for  making  deposits  of  salts,  and  for 
use  in  chemical  changes  attending  the  making  of  rocks 
and  minerals,  the  ocean  being,  so  to  speak,  the  largest  of 
mineral  springs. 

The  mechanical  effects  of  the  ocean  are  produced  by  its 
waves  and  currents. 


EROSION  AND  TRANSPORTATION. 

1.  Waves. — Greneral  Action. — The  force  in  oceanic 
waves  is  a  constant  force.  Night  and  day,  year  in  and 
year  out,  with  hardly  an  intermission,  they  break  against 
the  beaches  and  rocks  of  the  coast ;  sometimes  gently, 
sometimes  in  heavy  plunges  that  have  the  force  of  a 
Niagara  of  almost  unlimited  breadth.  The  gentlest 
movements  have  some  grinding  action  among  the  sands, 
while  the  heaviest  may  dislodge  and  move  along,  up  the 
shores,  rocks  many  tons  in  weight.  Niagara  wastes  its 
power  by  falling  into  an  abyss  of  waters  ;  but  in  the  case 
of  the  waves  the  rocks  are  bared  anew  for  each  successive 
plunge.  The  waters  are  often  loaded  with  gravel  and 
sand  when  they  strike,  and  thus  carry  on  abrasion.  Cliffs 
are  undermined,  rocks  are  worn  to  pebbles  and  sand,  and, 
through  mutual  friction,  sand  is  ground  to  the  finest  pow- 
der. Rocky  headlands  on  windward  coasts  are  especially 
exposed  to  wear,  since  they  are  open  to  the  battering  force 
Prom  different  directions. 


148  DYNAMICAL   GEOLOGY. 

Level  of  Greatest  Eroding  Action.  —  The  eroding  action 
is  greatest  for  a  short  distance  above  the  height  of 
half  tide,  and,  except  in  violent  storms,  it  is  almost  null 
below  low-tide  level.  Fig.  183  represents  in  profile  a 
cliff,  having  its  lower  layers,  near  the  level  of  low  tide,  ex- 
tending out  as  a  platform  a 
FlG-  183-  hundred  yards  wide.  As  the 

tide  commences  to  move  in, 
the  waters,  while  still  quiet, 
swell  over  and  cover  this 
platform,  and  so  give  it  their 

f,  New  south  Wales.  protection  ;  and  the  force  of 

wave  action,  which  is  great- 
est above  half  tide,  is  mainly  expended  near  the  base  of 
the  cliff,  just  above  the  level  of  the  platform.  But  to  give 
opportunity  for  much  battering  effect  a  coast  should  be 
shelving,  so  that  the  waters  may  advance  up  the  slope.  If 
the  water  is  deep  alongside  of  a  cliff,  there  is  simply  a 
rise  and  fall,  with  little  abrasion. 

Action  Landward.  —  Waves  on  shallow  soundings  have 
some  transporting  power ;  and,  as  they  always  move 
toward  the  land,  their  action  is  landward.  They  thus 
beat  back,  little  by  little,  any  detritus  in  the  waters,  pre- 
venting that  loss  to  continents  or  islands  which  would 
take  place  if  it  were  carried  out  to  sea. 

Effect  on  the  Outline  of  Coasts;  No  Excavation  of  Nar- 
row Valleys.  —  As  the  action  of  waves  on  a  coast  tends  to 
wear  away  headlands,  and  at  the  same  time  to  fill  up  bays 
with  detritus,  it  usually  results  in  making  the  outline  more 
regular  or  even.  There  is  nowhere  a  tendency  to  exca- 
vate narrow  valleys  into  a  coast,  like  those  occupied  by 
rivers.  Such  valleys  are  made  by  the  waters  of  the  land. 
If  a  continent  were  sinking  slowly  in  the  ocean,  or  rising 
slowly  from  it,  wave  action  would  still  be  attended  by  the 
same  results  ;  for  each  part  of  the  surface  would  be  suc- 
cessively a  coast  line,  and  over  each  there  would  be  the 
same  wearing  away  of  headlands,  and  filling  of  bays,  in- 


MECHANICAL   EFFECTS   OF   WATER.  149 

stead  of  the  excavation  of  valleys.  The  chasms,  or  "  pur- 
gatories," sometimes  made  on  a  rocky  coast,  where  a  dike 
of  trap,  or  a  thin  slice  of  rock  included  between  parallel 
joints,  yields  to  the  disintegrating  action  of  the  waves,  are 
of  course  readily  distinguished  from  true  valleys. 

2.  Tidal  Currents.  —  Tidal  currents  often  have  great 
strength  when  the  tide  moves  through  channels  or  among 
islands,  and  then  they  are  a  means  of  erosion  and  trans- 
portation daily  in  action,  wherever  there  is  rock,  mud,  or 
sand  within  their  reach. 

The  outflowing  current  from  bays,  or  that  connected 
with  the  ebbing  tide,  is  deeper  in  its  action,  and  has, 
therefore,  more  excavating  and  more  transporting  power 
than  the  inflowing,  or  that  of  the  incoming  tide.  The 
latter  moves  on  as  a  great  swelling  wave,  and  fills  the 
bays  much  above  their  natural  level ;  but  the  outflowing 
current  begins  along  the  bottom  before  the  tide  is  wholly 
in,  owing  to  the  accumulation  of  waters  ;  and,  when  the 
tide  changes,  it  adds  to  the  strong  current  movement 
already  in  progress. 

The  piling  up  of  the  waters  in  a  bay  by  the  tides,  or  by 
storms,  produces,  especially  if  the  entrance  is  not  very 
broad,  a  strong  outflowing  current  at  bottom,  which  tends 
to  keep  the  channel  deep  and  clear  of  obstructions. 

The  inflowing  tide,  sweeping  along  a  coast,  checks  partly 
or  wholly  the  outflow  of  the  rivers.  This  causes  the  depo- 
sition of  more  or  less  of  the  detritus  which  the  rivers 
transport,  near  or  against  the  shores  or  flats  just  beyond 
the  river  channel ;  and  thus  it  often  makes  great  sand 
flats,  which  encroach  on  the  entrance.  If  a  long  point 
projects  on  the  side  of  the  mouth  first  reached  by  the  in- 
flowing tide,  the  tidal  flow  may  carry  the  detritus  far 
beyond  the  river's  mouth  ;  but,  if  no  such  point  exists, 
and  the  opposite  cape  is  the  longer,  the  detritus  will  be 
thrown  into  the  throat  of  the  stream,  and  the  entrance 
become  more  or  less  choked.  The  river  mouths  of  the 
Connecticut  shore,  on  the  north  side  of  Long  Island 


150  DYNAMICAL  GEOLOGY. 

Sound,  along  which  the  inflowing  tide  moves  westward, 
well  illustrate  these  facts.  The  two  largest  of  the  rivers, 
the  Connecticut  and  Housatonic,  are  of  the  unfortunate 
kind,  as  they  have  no  eastern  cape  ;  while  the  harbor  of 
New  Haven,  although  it  receives  only  very  small  streams, 
is  much  better  off,  as  regards  depth  of  water  for  entrance, 
because  of  a  projecting  eastern  cape. 

The  bore,  or  eager,  of  some  great  rivers  is  a  kind  of  tidal 
flow  up  a  stream.  It  is  produced  when  the  regular  rise 
of  the  tide  in  the  bay  at  the  mouth  of  the  river  is  ob- 
structed by  the  form  of  the  entrance  and  its  sand  banks, 
together  with  the  outflow  of  the  river,  so  that  the  waters 
are  for  a  while  prevented  from  entering,  until,  finally,  all 
those  of  one  tide  rush  in  at  once,  or  in  a  few  great  waves. 
The  eagers  of  the  Amazon,  the  Hoogly  in  India  (one  of 
the  mouths  of  the  Ganges),  and  the  Tsien-tang  in  China, 
are  among  the  most  remarkable.  In  the  case  of  the  Tsien- 
tang,  the  water  moves  up  stream  in  one  great  wave,  plung- 
ing like  an  advancing  cataract,  four  or  five  miles  broad 
and  30  feet  high,  at  a  rate  of  25  miles  an  hour.  The 
boats  in  the  Middle  of  the  stream  simply  rise  and  fall  with 
the  passage  of  the  wave,  being  pushed  forward  only  a 
short  distance  ;  but  along  the  shores  there  is  often  great 
devastation,  the  banks  being  worn  away,  and  animals 
sometimes  surprised  and  destroyed. 

3.  Currents  made  by  Winds.  —  The  great  currents  of  the 
ocean,  such  as  the  Gulf  Stream,  are  attributed  by  most 
physicists  to  this  source.  But,  besides  these,  there  are 
local  currents  along  many  coasts  produced  by  winds,  espe- 
cially when  there  are  long  and  violent  storms,  or  winds 
blowing  for  months  in  one  direction.  Such  currents, 
sweeping  by  a  coast,  transport  from  one  place  to  another 
in  their  course  more  or  less  of  the  sand  of  the  shores, 
often  making  long  sand  flats  or  spits  off  the  shores  to  lee- 
ward, as  on  the  south  coast  of  Long  Island  and  along  the 
more  southern  parts  of  the  Atlantic  border.  The  action 
is  aided  by  the  tidal  currents.  In  some  cases  the  drifted 


MECHANICAL  EFFECTS   OF  WATER.  151 

sand  may  be  in  part  carried  back  again  when  the  season 
changes  to  that  in  which  the  wind  blows  from  the 
opposite  direction.  Other  portions  of  detritus  may  be 
carried  away  from  the  land  and  distributed  in  the  deeper 
waters. 

The  great  currents  of  the  ocean  are  for  the  most  part  so 
distant  from  the  borders  of  the  continents  that  little  de- 
tritus comes  within  their  reach.  As  these  currents  have 
great  depth  —  often  a  thousand  feet  or  more,  —  their 
course  is  determined  partly  by  the  deep-water  slopes  of 
the  submerged  border  of  a  continent,  so  that,  when  the 
border  is  shallow  for  a  long  distance  out  (as  off  New 
Jersey  and  Virginia,  where  this  distance  is  even  50 
to  80  miles),  the  main  body  of  the  current  is  equally 
remote.  Wherever  it  actually  sweeps  close  along  a  coast, 
it  may  bear  away  some  detritus,  to  drop  it  over  the  bot- 
tom in  the  neighboring  waters.  The  flow  of  the  Gulf 
Stream  against  the  submerged  slope  of  the  oceanic  basin 
(at  the  rate  of  a  mile  or  more  per-  hour)  is  sufficient  to 
keep  the  bottom  free  from  loose  detritus.  Verrill  has 
suggested  that  the  burrowing  of  fishes  for  food  aids  the 
erosive  action  of  currents,  by  loosening  the  material. 

The  oceanic  currents  flowing  from  polar  seas  produce 
important  effects  by  means  of  the  icebergs  which  they  bear 
into  warmer  latitudes.  These  icebergs  are  sometimes 
freighted  with  earth  and  rocks  ;  and,  wherever  they  melt, 
they  drop  all  to  the  ocean's  bottom.  The  sea  about  the 
Newfoundland  banks  is  one  of  the  regions  of  melting 
icebergs ;  and  there  is  no  doubt  that  vast  submarine  ac- 
cumulations of  such  material  have  been  made  there  by 
this  means. 

DISTRIBUTION  OF  MATERIAL,  AND  FORMATION  OF  MARINE 
AND  FLUVIO-MARINE  DEPOSITS. 

Origin  of  Material.  —  The  material  used  by  the  waves 
and  currents  is  either  —  (1)  the  stones,  gravel,  sand,  clay, 
or  earth  produced  by  the  wear  of  coasts  ;  or  (2)  the.  detri- 


152  DYNAMICAL  GEOLOGY. 

tus  brought  down  by  rivers  and  poured  into  the  ocean,  as 
explained  on  pages  136-140. 

The  latter,  in  the  present  age,  is  by  far  the  more  im- 
portant. But  in  the  earlier  geological  ages,  when  the  dry 
land  was  of  small  extent,  rivers  were  small  and  were  but 
a  feeble  agency. 

The  decomposition  or  disintegration  of  exposed  rocks 
through  the  agency  of  air  and  moisture  must  have  aided 
in  degradation  formerly  more  than  now,  since,  in  Paleozoic 
time  and  earlier,  carbonic  acid,  the  chief  agent  of  destruc- 
tion, was  much  more  abundant  in  the  atmosphere  than  it 
is  now.  This  agent  is  carried  to  the  earth's  surface  by 
the  rains,  and  it  is  still  effective  in  the  decomposition  of 
granite,  gneiss,  and  many  other  rocks.  The  higher  tem- 
perature of  the  atmosphere  in  early  geological  times  was 
also  favorable  to  rapid  chemical  action. 

Forces  in  Action.  —  In  the  distribution  of  the  materiaj, 
the  waves  and  marine  currents  have  either  worked  alone, 
in  the  manner  explained  on  the  preceding  pages,  or  in 
conjunction  with  river  currents  wherever  these  existed. 

Marine  Formations.  —  The  marine  formations  are  of  the 
following  kinds  :  — 

1.  Beach  Accumulations.  — Beaches  are  made  of  the  ma- 
terial borne  up  the  shores  by  the  waves  and  tides  and  left 
above  low-tide  level.     This  material  consists  of  stones  or 
pebbles,  sand,  mud,  earth,  or  clay.     It  is  coarse  where  the 
waves  break  heavily,  because,  although  trituration  to  pow- 
der is  going  on  at  all  times,  the  powerful  wave  action  and 
the  undercurrent  carry  off  the  finer  material  into  the  off- 
shore shallow  waters,  where  it  settles  over  the  bottom  or 
is  distributed  by  currents.     It  is  fine  where  the  waves  are 
gentle  in  movement,  as  in  sheltered  bays,  or  estuaries,  the 
triturated  material  remaining  in  such  places  near  where  it 
is  made,  and  often  being  the  finest  of  mud. 

2.  Sand  Banks,  or  Reefs;  Shallow-water  Accumulations. 
—  Shallow-water  accumulations  may  be  produced  in  bays, 
estuaries,  or  the  inner  channels  of  a  coast,  and  over  the 


MECHANICAL   EFFECTS    OF   WATER. 


153 


FIG.  184. 


bottom  outside.  They  consist  usually  of  coarse  or  fine 
sand  and  earthy  detritus,  but  may  include  pebbles  or 
stones  when  the  currents  are  strong.  The  material  consti- 
tuting them  is  derived  from  the  land  through  the  wearing 
and  transporting  action  either  of  the  waves  and  currents 
or  of  rivers.  The  accumulations  may  increase  under  wave 
action  in  shallow  water,  until  they  approach  or  rise  above 
low-tide  level,  and  then  they  form  sand  banks.  Such  sand 
banks  keep  their  place  in  the  face  of  the  waves,  for  the 
same  reason  as  the  platform  of  rock  mentioned  on  page  148 
and  illustrated  in  Fig.  183. 

3.  Fluvio-marine  Formations.  —  Most  of  the  accumula- 
tions in  progress  on  existing  shores,  whether  sand  banks, 
or  estuarine,  or  off-shore  deposits,  especially  about  well- 
watered  continents,  contain  more  or  less  of  river  detritus, 
and  are  modified  in  their  forms  by 
the  action  of  river  currents.  Along 
the  whole  eastern  coast  of  the 
United  States  south  of  New  Eng- 
land, and  on  all  the  borders  of  the 
Gulf  of  Mexico,  the  formations  in 
progress  are  mainly  fluvio-marine  —  that  is,  the  combined 
result  of  rivers  and  the  ocean.  The  coast  region  of  the 
continent  is  now  slowly  widening  through  this  means, 
and  has  been  widening  for  an  indefinite  period.  This 
coast  region  is  low,  flat,  often  marshy,  full  of  channels  or 
sounds ;  and  facing  the  ocean  there  is  a  barrier  of  sand. 

The  rivers  pour  out  their  detritus  especially  during  their 
floods,  and  the  ocean's  waves  and  currents  meet  it  as  the 
tide  sets  in,  with  a  counter  action,  or  one  from  the  sea 
landward  ;  between  the  two,  the  waters,  as  they  lose  their 
velocity,  drop  the  detritus  over  the  bottom.  Where  the 
river  is  very  large  and  the  tides  feeble,  the  banks  and  reefs 
extend  far  out  to  sea.  The  Mississippi  thus  stretches  its 
many-branched  mouth  (Fig.  180)  fifty  miles  into  the  Gulf. 
Where  the  tide  is  strong,  sand  bars  are  formed  ;  and  the 
stronger  the  tides,  the  closer  are  the  sand  bars  to  the  coast. 


Beach  structure. 


154  DYNAMICAL   GEOLOGY. 

Where  the  stream  is  small,  the  ocean  may  throw  a  sand- 
bank quite  across  its  mouth,  so  that  there  may  be  no  egress 
to  the  river  waters  except  by  percolation  through  the  sand; 
or,  if  a  channel  is  left  open,  it  may  be  only  a  shallow  one. 

STRUCTURE  OP  THE  FORMATIONS. 

Beach  Formations  are  very  irregular  in  stratification  in 
their  upper  portions,  where  they  are  made  by  the  toss  of 
the  waves  combined  with  drifting  by  the  winds.  The 
layers  —  as  shown  in  Fig.  184  —  have  but  little  lateral  ex- 
tent, and  change  in  character  every  few  feet.  But  the 

sloping  part  swept  by  the 

FIG.  185.  "Y   1  u-    iT  a.-  i 

waves  below  high-tide 
level  is  very  evenly  strati- 
fied parallel  to  the  sur- 
face ;  and,  since  this  sur- 
face dips  usually  at  an 
angle  of  5°  to  15°,  the 
beach-made  beds  have  the 
same  dip.  The  coarsest 
beaches  have  the  steepest 
slopes. 

The  sand  banks  and 
reefs  made  in  shallow 
waters  along  a  coast  have 

Eipple-marks. 

a  more  regular  and  more 

nearly  horizontal  stratification,  and  are  mostly  composed 
of  sand  with  some  beds  of  pebbles.  They  often  vary 
much  every  mile  or  every  few  miles.  The  extent  and 
regularity  of  level  of  the  submerged  area  off  a  coast  will 
determine  in  a  great  degree  the  extent  to  which  the  uni- 
formity of  stratification  may  extend ;  and,  in  this  respect, 
the  conditions  were  much  more  favorable  for  the  deposit 
of  uniformly  stratified  sediments  over  wide  areas  in  for- 
mer geological  ages  than  at  present,  since  large  areas  of 
the  continents  were  formerly  submerged  at  shallow  depths. 


MECHANICAL  EFFECTS   OF   WATER. 


155 


FIG.  186. 


I 


Ripple-marks  (Fig.  185)  are  alternate  ridges  and  fur- 
rows made  by  the  wash  of  the  waters  over  a  sand  flat 
or  beach,  or  over  the  bottom  within  soundings.  They 
may  also  be  made  by  the  action  of  wind  on  fields  of  sand. 
The  width  of  the  furrows  may 
be  a  fraction  of  an  inch,  or 
several  inches.  Rill-marks  (Fig. 
186)  are  produced  when  the 
return  waters  of  a  tide,  or  of 
a  wave  that  has  broken  on  a 
beach,  flow  by  an  obstacle,  as 
a  shell  or  pebble,  and  are  piled 
up  a  little  by  it,  so  as  to  be  made 
to  plunge  over  it,  and  so  erode 
the  sands  for  a  short  distance 
below  the  obstacle.  The  figure 
shows  such  markings  in  con- 
nection with  shells  (Lingula) 
in  a  Silurian  sandstone. 

The  cross-bedded  structure  (Fig.  187)  is  characterized 
by  lamination  or  straticulation  in  a  plane  oblique  to  that 
of  the  stratification.  It  results  from  the  pushing  along  of 
the  sand  or  earth  by  currents,  causing  at  first  a  little  ele- 
vation, and  then  the  deposition 
of  successive  layers  over  the 
front,  or  down-stream,  slope  of 
the  elevation.  If  the  currents 
are  transient,  alternating  with 
conditions  of  still  water,  the 
obliquely  laminated  beds  will 
alternate  with  others  horizon- 
tally laminated.  Such  alternations  may  be  due  to  changes 
of  tide,  or  to  the  periodical  or  occasional  fluctuations  in  the 
volume  of  rivers.  When  there  are  plunging  waves  accom- 
panying the  rapid  flow  of  a  current,  the  obliquely  laminated 
layer  is  broken  up  into  short,  wavelike  parts, — as  in  the 
flow-and-plunge  structure  (Fig.  188). 


Eill-marks. 


FIG.  187. 


Cross-bedded  structure. 


156 


DYNAMICAL  GEOLOGY. 


Mud-cracks,  Earth-cracks.  —  When  a  mud  flat  is  ex- 
posed to  the  air  or  sun  to  dry,  as  by  the  ebbing  of  a  tide 
or  the  subsiding  of  a  freshet,  it  becomes  cracked  to  a  few 
inches  or  feet  in  depth.  Fig.  189  represents  mud-cracks 
in  argillaceous  sandstone.  Such  cracks  may  subsequently 

FIG.  188. 


Flow-and-plunge  structure. 

become  filled  with  stony  material,  either  sediment  or 
material  in  solution  ;  and,  as  such  fillings  are  often  harder 
than  the  rock  itself,  they  may  stand  as  prominent  ridges 
above  a  weathered  surface  of  the  rock.  It  is  actually  a 

FIG.  189. 


Mud-cracks. 

network  of  veins,  but  of  very  shallow  veins  that  were 
filled  from  above.  In  regions  of  long  droughts,  the  earth- 
cracks  over  prairies  and  alluvial  flats  are  sometimes  many 
and  deep,  and  over  a  foot  wide. 

The  imbedded  shells  and  other  animal  relics  in  a  beach 
are   commonly   broken ;    those   in   the   bays   or   offshore 


MECHANICAL  EFFECTS   OF  WATER.  157 

waters  out  of  the  reach  of  the  waves  may  be  unbroken, 
or  may  lie  as  they  did  when  living ;  but,  if  the  waters 
are  so  shallow  that  the  shells  or  corals  are  exposed  to 
wave  action,  they  may  be  broken  or  worn  to  powder,  and 
enter  in  this  state  into  the  formation  in  progress.  (See 
pages  99-105  for  further  discussion  of  the  formation  of 
limestone  from  shells  or  corals.) 

Deposits  of  broken  shells  under  water  are  sometimes 
made  by  Fishes  that  have  taken  the  animals  for  food. 
Such  beds  made  by  Fishes  answer  to  the  shell  heaps  of 
human  origin. 

In  the  sands  of  beaches  near  low-tide  level,  borings 
of  Worms,  Mollusks,  or  Crustaceans,  may  exist ;  and,  if 
sand  or  mud  is  left  above  the  water  level,  as  by  the  re- 
ceding tide,  it  may  be  marked  by  tracks  of  various  land 
animals. 

3.    Freezing  and  Frozen  Waters. 

Freezing  Water.  —  As  water  in  the  act  of  freezing  ex- 
pands after  reaching  39.2°  F.  (4°  C.),  freezing  in  the 
seams  of  rock  opens  the  seams  and  tears  masses  asunder. 
The  expansion  on  reaching  32°  F.  is  -^  lineally,  and  the 
density  is  diminished  to  0.92.  The  results  of  expansion 
are  most  marked  in  rocks  that  are  much  fissured,  or 
intersected  by  joints,  or  that  have  a  slaty  or  laminated 
structure.  As  the  action  continues  through  successive 
years  and  centuries,  it  often  results  in  great  accumula- 
tions of  broken  stone.  The  slope,  or  talus,  of  fragments 
at  the  foot  of  a  cliff  of  trap  or  basalt  is  often  more  than 
half  as  high  as  the  cliff  itself.  In  tropical  countries, 
cliffs  have  no  such  masses  of  ruins  at  their  base. 

Granular  rocks,  whether  crystalline  or  not,  when  they 
readily  absorb  water,  lose  their  surface  grains  by  the  same 
freezing  process.  Granite,  as  well  as  porous  sandstones, 
may  thus  be  imperceptibly  turning  to  dust,  earth,  or 
gravel.  In  Alpine  regions  this  action  may  be  incessant. 

Alternate  freezing  and  thawing  produces  (as  explained 


158  DYNAMICAL   GEOLOGY. 

by  Kerr)  a  downward  movement  of  earth  and  gravel  on 
slopes,  with  rearrangement  of  the  materials. 

Frozen  Water.  —  The  effects  of  ice  and  snow  are  con- 
veniently considered  under  three  heads :  —  1,  The  Ice  of 
Lakes  and  Rivers ;  2,  Glaciers ;  3,  Icebergs. 

1.  ICE  OF  LAKES  AND  RIVERS. 

The  ice  of  lakes  and  rivers  often  forms  about  stones 
along  their  shores,  and  sometimes  over  those  of  the  bot- 
tom (then  called  anchor  ice),  making  them  part  of  the 
mass  ;  and  other  stones  sometimes  fall  on  shore  ice  from 
overhanging  bluffs.  The  ice  serves  as  a  float  to  the 
stones  ;  and  in  times  of  high  water,  or  floods,  it  may 
carry  its  burdens  high  up  the  shores,  or  over  the  flooded 
flats,  to  leave  them  there  as  it  melts.  Large  accumula- 
tions of  bowlders  are  sometimes  made,  by  this  means,  on 
shores  far  above  the  ordinary  level  of  the  waters. 

2.  GLACIERS. 

Glaciers  are  Ice  Streams,  or  rivers  in  which  the  moving 
material  is  frozen  instead  of  liquid  water. 

Like  large  rivers,  they  ordinarily  have  their  sources 
in  high  mountains,  and  descend  along  the  valleys ;  but 
(1)  the  mountains  must  be  high  enough  to  receive  snow 
from  the  clouds  instead  of  rain ;  and  (2)  they  must  be 
extensive  enough  to  receive  annually  a  large  supply  of» 
snow,  so  that  it  may  accumulate  to  a  great  depth ;  and 
(3)  the  region  must  be  one  of  sufficient  precipitation. 

As  in  the  case  of  rivers,  many  tributary  streams  coming 
from  the  different  valleys  may  unite  to  make  the  great 
stream. 

As  with  rivers,  their  movement  is  dependent  on  gravity, 
or  the  weight  of  the  material ;  but  the  average  rate  of 
motion,  instead  of  being  several  miles  an  hour,  is  generally 
in  summer  but  10  to  18  inches  a  day,  or  a  mile  in  18  to 
20  years.  Twelve  inches  a  day  corresponds "  to  a  mile 


MECHANICAL  EFFECTS   OF   WATEE.  159 

in  141  years.  The  rate  in  winter  is  about  half  of  that  in 
summer. 

As  with  rivers,  the  central  portions  move  most  rapidly, 
the  sides  and  bottom  being  retarded  by  friction. 

The  snow  of  the  mountain  tops,  called  n£v€,  or  firn, 
which  is  perhaps  hundreds  of  feet  deep,  becomes  com- 
pacted and  converted  into  ice  mainly  by  its  own  weight, 
with  the  aid  of  water  penetrating  it,  derived  from  partial 
melting  ;  and  thus  the  glacier  begins.  Through  alternate 
melting  and  freezing,  the  change  to  ice  is  made  more 
complete.  As  the  glacier  starts  on  its  course,  the  clouds 
furnish  new  snows  to  keep  up  the  supply  and  help  press 
on  the  moving  mass. 

Descent  below  the  Snow  Line.  —  The  height,  in  the 
Alps,  of  the  snow-line,  or  that  below  which  the  snow 
annually  precipitated  melts  during  the  year,  is  about  8400 
feet  on  the  north  side  of  the  Alps,  and  about  8800  feet  on 
the  south  side  ;  and  the  glacier  may  descend  below  this 
line  5000  feet  or  more.  The  ice  resists  the  melting  heat 
of  summer  because  of  its  mass,  like  the  ice  in  an  ice-house. 
Though  starting  where  all  is  white  and  barren,  it  passes 
by  regions  of  Alpine  flowers,  and  often  continues  down  to 
a  country  of  gardens  and  human  dwellings  before  its  course 
is  ended.  Thus,  the  Grlacier  des  Bois,  an  upper  portion  of 
which  is  called  the  Mer  de  Grlace,  rises  in  Mont  Blanc  and 
other  neighboring  peaks,  and  terminates,  like  several  other 
glaciers,  in  the  vale  of  Chamouni.  In  a  similar  manner, 
two  great  glaciers  descend  from  the  heights  of  the  Bernese 
Alps  to  the  Grindelwald  valley  just  south  of  Interlaken. 

Fig.  191  represents  one  of  the  ice  streams  of  the  Monte 
Rosa  region  in  the  Alps,  from  a  view  in  Professor 
Agassiz's  work  on  Glaciers.  It  shows  the  lofty  regions 
of  perpetual  snow  in  the  distance  ;  the  bare  rocky  slopes 
that  border  it,  later  on  its  course  ;  and  the  many  crevasses 
that  intersect  the  surface  of  the  ice  stream. 

Fractures  attending  the  Movement ;  Crevasses.  —  Every 
valley  has  its  ridgy  sides,  its  sharp  turns,  its  abrupt  nar- 


160  DYNAMICAL   GEOLOGY. 

rowings  and  widenings,  its  irregular  bottom  ;  and  the  stiff 
ice,  compelled  to  accommodate  itself  to  these  irregularities, 
forms  by  its  rupture  profound  crevasses,  besides  multi- 
tudes of  cracks  that  are  not  visible  at  the  surface.  There 
are  crevasses  on  the  convex  side  of  every  bend  in  the 
glacier ;  transverse  crevasses,  crossing  even  its  whole 
breadth,  where  the  ice  plunges  down  a  steep  place  in  an 
ice  cascade  ;  and  longitudinal  crevasses,  where  the  ice, 
escaping  from  a  narrow  gorge,  spreads  laterally  over  a 
broad  valley  or  plain.  Independently  of  any  local  irregu- 
larities, the  more  rapid  motion  of  the  central  part  of  a 
glacier  causes  a  diagonal  strain  (theoretically  in  a  direc- 
tion at  an  angle  of  45°  with  the  axis  of  the 

FIG.  190.  .  .  &  . 

glacier},  which  produces  a  series  or  marginal 
crevasses,  having  the  direction  indicated  by 
Fig.  190. 

Again,  crevasses  once  formed  may  close  up 
again,  when  the  form  of  the  valley  is  such 
that   a    portion    of   the    ice    is    subjected    to 
pressure  in  a  direction  in  which  it  has  formerly 
Diagram  niustrat-  been  subjected  to  tension, 
mg  marginal        Glacier  Torrent.  —  The  melting  of  the  gla- 

crevasses.  .  ° 

cier,  especially  during  the  warm  season,  gives 
rise  to  streams  of  Water  flowing  beneath  it,  which  finally 
unite  in  a  torrent  of  considerable  size,  emerging  to  the 
light  from  beneath  the  bluff  of  ice  in  which  the  glacier 
terminates.  Thence  it  continues  on  its  rocky  course  down 
the  valley. 

Method  of  Movement.  —  The  capability  of  motion  in  a 
glacier  is  dependent  (1)  partly  on  a  degree  of  plasticity 
in  ice.  Ice  may  be  made,  through  pressure,  to  copy  a 
seal,  or  may  be  drawn  out  into  cylinders  ;  or,  if  a  slab  is 
supported  only  at  the  sides,  it  will  become  bent  downward, 
through  gravity.  The  apparent  plasticity  of  glacier  ice  is, 
however,  in  great  part  due  to  the  processes  referred  to  in 
the  next  two  paragraphs. 

(2)  The  movement  depends  in  great  part  upon  the  facil- 


MECHANICAL   EFFECTS    OF    WATER. 


161 


ity  with  which  ice  breaks,  and  afterwards  reunites  into  a 
solid  mass  when  the  broken  surfaces  are  brought  into  con- 
tact. This  property  of  regelation  was  first  noticed  by 
Faraday.  It  is  easily  shown  by  breaking  a  lump  of  ice 
and  bringing  the  surfaces  again  jnto  contact:  if  moist,  as 
they  are  at  the  ordinary  temperature,  they  at  once  become 
firmly  united.  A  glacier  moves  on  and  accommodates 

FIG.  191. 


Glacier  of  Zermatt,  or  Gorner  Glacier. 

itself  to  its  uneven  bed  by  breaking ;  and,  however  frac- 
tured it  may  be,  it  becomes,  when  the  parts  are  pressed 
together,  as  solid  as  before. 

(3)  The  movement  of  the  ice  is  facilitated  by  alter- 
nate melting  and  freezing  in  the  interior  of  the  glacier. 
The  crystalline  grains  of  which  the  glacier  is  composed, 
are  found  to  increase  from  the  almost  microscopic  size  of 


162  DYNAMICAL   GEOLOGY. 

the  crystals  of  the  snowflakes  on  the  mountain  summits 
to  a  diameter  of  several  inches  near  the  end  of  a  glacier; 
and  this  indicates  a  great  amount  of  melting  and  freezing. 
This  process  goes  on  most  rapidly  when  the  greatest 
amount  of  heat  is  communicated  to  the  glacier.  Hence 
the  motion  is  more  rapid  in  summer  than  in  winter. 

(4)  A  glacier  may,  here  and  there,  at  times,  slide  along 
its  bed,  yet  only  portions  at  a  time. 

Transportation  by  Glaciers ;  Moraines.  —  Glaciers  be- 
come laden  with  stones  and  earth  falling  from  the  heights 
above,  or  coming  down  in  avalanches  of  snow  and  stones. 
The  stones  and  earth  make  a  band  along  either  border  of 
a  glacier,  and  such  a  band  is  called  a  moraine.  When  two 
glaciers  unite,  they  carry  forward  their  bands  of  stones 
with  them ;  but  those  on  the  uniting  sides  combine  to 
make  one  moraine,  which  is  called  a  medial  moraine,  in 
distinction  'from  the  lateral  moraines  on  the  margins  of 
the  glacier.  A  large  glacier,  like  that  in  Fig.  191,  may 
have  many  moraines  —  one  more  than  the  number  of  trib- 
utaries by  whose  union  the  trunk  glacier  has  been  formed. 

In  the  lower  part  of  a  glacier  the  several  moraines  gen- 
erally lose  their  distinctness,  through  the  melting  of  the 
ice,  and  also  by  reason  of  the  fact  that  the  glacier  is  gen- 
erally compressed  in  its  lower  part  to  a  width  very  much 
less  than  the  aggregate  width  of  its  tributaries.  The  sur- 
face of  the  glacier,  accordingly,  often  becomes  covered 
with  earth  and  stones  for  the  greater  part  of  its  breadth. 
The  bluff  of  ice  which  forms  the  foot  of  a  glacier  is  often 
a  dirty  mass,  scarcely  revealing  superficially  its  real  nature. 

Some  of  the  masses  of  rock  on  glaciers  are  of  immense 
size.  One  is  mentioned  containing  over  200,000  cubic  feet 
—  which  is  equivalent  in  cubic  contents  to  a  building  100 
feet  long,  50  feet  wide,  and  40  feet  high. 

Besides  the  superficial  moraines,  a  glacier  also  gathers 
rock  material  from  the  bottom  over  which  it  moves.  The 
disintegrated  and  decomposed  rock  is  mostly  scraped  from 
the  surface,  masses  of  rock  are  torn  off  from  jointed  ledges, 


MECHANICAL   EFFECTS   OF   WATER. 


163 


and  soft  rocks  in  the  path  of  the  glacier  are  deeply  abraded. 
The  materials  thus  gathered  from  the  bed  of  the  glacier, 
with  additions  from  stones  which  have  fallen  into  the 
crevasses  from  above,  form  the  ground  moraine,  or  moraine 
profonde. 

The  final  melting  leaves  all  the  earth  and  stones  in  un- 
stratified  heaps  or  deposits,  which  may  be  further  trans- 
ported, abraded,  and  deposited,  by  the  stream  that  flows 

FIG.  192. 


View  on  Koche-moutoimee  Creek,  Colorado. 

from  the  glacier.     The  mass  of  such  deposits  dropped  at 
the  foot  of  a  glacier  is  called  the  terminal  moraine. 

Erosion  by  Glaciers.  — A  glacier  laden  with  stones 
will  have  stones  in  its  lower  surface  and  sides,  as  well  as 
in  its  mass.  As  it  moves  down  the  valley,  it  consequently 
abrades  the  exposed  rocks  over  which  it  passes,  smoothing 
and  polishing  some  surfaces,  covering  others  closely  with 
parallel  scratches,  and  often  plowing  out  broad  and  deep 


164  DYNAMICAL   GEOLOGY. 

channels,  besides  having  its  abrading  bowlders  scratched 
or  polished. 

Deep  plowing  is  accomplished  chiefly  (1)  where  the  rock 
beneath  is  soft  or  fragile,  or  (2)  where  it  is  jointed,  rifted, 
or  laminated.  In  the  latter  case  the  action  is  rending, 
rather  than  abrading,  and  by  this  means  the  larger  part  of 
the  direct  excavation  by  glaciers  has  been  done. 

The  rocky  ledges  over  which  the  ice  has  moved  are 
often  reduced  to  rounded  prominences ;  they  then  look,  in 
the  distance,  like  groups  of  crouching  sheep,  and  hence 
have  been  called,  in  French,  roches  moutonnges.  They  are 
exhibited  on  a  grand  scale  in  some  of  the  valleys  of  the 
high  ranges  along  the  summit  of  the  Rocky  Mountains, 
where  were  formerly  extensive  glaciers ;  and  Fig.  192 
represents  such  a  scene,  in  the  region  of  the  Mountain 
of  the  Holy  Cross  (the  remote  summit  near  the  center 
of  the  view),  as  photographed  by  the  photographer  of  the 
expedition  under  Dr.  Hayden.  Further,  the  stones  in 
the  ever-shifting  ice  are  worn,  and  become  rounded  at  the 
angles  ;  and  the  very  fine  rock  flour  derived  in  part  from 
the  transported  stones  and  in  part  from  the  bed  rock,  is 
carried  down  by  the  glacier  torrent,  to  make  beds  of  clay 
or  earth,  and  give  a  milky  hue  to  the  rivers  flowing  from 
a  glacier  region. 

Glaciers  deepen  and  widen  the  valleys  in  which  they 
move.  But  in  this  work  they  are  aided  by  frosts,  ava- 
lanches, and  especially  by  the  torrents  beneath  the  glacier. 

Glacier  Regions.  —  The  best  known  of  Glacier  regions 
are  those  of  the  Alps,  in  one  of  which  Mont  Blanc  stands, 
with  its  summit  15,760  feet  above  the  sea.  There  are 
glaciers  also  in  the  Pyrenees,  the  mountains  of  Norway, 
Spitzbergen,  Greenland,  Alaska,  and  other  Arctic  regions, 
in  the  Caucasus  and  Himalaya,  in  the  southern  Andes,  in 
the  Cascade  Range,  and  in  the  Rocky  Mountains  of  British 
America.  Greenland  is  a  great  glacier-covered  land,  send- 
ing many  large  streams  of  ice  through  the  fiords  of  the 
border  region  to  the  polar  seas. 


MECHANICAL   EFFECTS   OF   WATER.  165 


3.  ICEBERGS. 

When  glaciers,  like  those  of  Greenland,  terminate  in 
the  sea,  the  icy  foot  becomes  broken  off  from  time  to  time ; 
and  these  fragments  of  glaciers,  floated  away  by  the  sea, 
are  icebergs.  The  geological  effects  of  icebergs  have  been 
stated  on  page  151.  Seashore  ice  sometimes  carries  stones 
and  gravel  far  out  to  sea. 

Summary.    Formation  of  Sedimentary  Strata. 

The  following  is  a  brief  recapitulation  of  the  explana- 
tions of  the  origin  of  deposits  given  in  the  preceding 
pages.  Igneous  and  other  crystalline  rocks  are  not  here 
included. 

1.  Sources  of  Material.  —  The  greater  part  of  the  ma- 
terial of  sedimentary  rocks  has  come  from  the  degradation 
of  preexisting  rocks.      But   another  part   (as  limestone 
and  infusorial  earth)  has  been  taken  up  from  a  state  of 
solution  in   the   ocean  or  in  fresh  waters,  through   the 
agency  of  life ;  yet  the  waters  have  received  the  ingredi- 
ents from  the  rocks,  either  when  the  ocean  first  began  to 
exist,  or  subsequently  through  the    dissolving  action  of 
streams  on  exposed  rocks  (page  137). 

2.  Means    of   Degradation.  —  The   principal   means   of 
degradation  are  the  following  :  —  (1)  Erosion  by  moving 
waters,  either  those  of  the  sea  or  land  (pages  126,  147); 
(2)  Erosion  by  ice,  chiefly  in  the  condition  of  glaciers  (page 
163);   (3)  Pressure  of  the  water  descending  into  fissures; 
(4)  Formation  of  substances,  for  example  oxide  of  iron,  in 
cracks,  tending  to  open  and  deepen  the  cracks ;  (5)  Growth 
of  rootlets,  roots,  and  trunks  of  trees,  in  crevices,  result- 
ing in  opening  and  tearing  apart  rocks,  and  often  produc- 
ing extensive  destruction  of  rocks,  especially  when  they 
are  jointed  ;   (6)  Freezing  of  water  in  fissures  (page  157); 
(7)  Chemical  decomposition  of  one  or  more  of  the  ingre- 
dients of  a  rock,  in  the  course  of  which  process  the  rock 


166  DYNAMICAL   GEOLOGY. 

becomes  crumbled  or  reduced  to  earth ;  (8)  Removal  by 
solution,  as  of  limestones  by  carbonated  waters  ;  (9)  Un- 
dermining of  rocks  by  any  method  ;  (10)  Expansion  and 
contraction  by  heat  (page  172). 

3.  Formation  of  Deposits.  —  The  principal  methods  by 
which  deposits  have  been  formed  are  the  following  :  — 

1.  By  the  Waters  of  the  Sea. —  (1)  Through  the  sweep 
of  the  ocean  over  the  submerged  portions  of  the  continents 
(pages  12, 154) :  —  making  sandy  or  pebbly  deposits  near  or 
at  the  surface  where  the  waves  strike,  or  at  very  shallow 
depths  where  swept  by  a  strong  current ;  argillaceous  or 
shaly  deposits  near  or  at  the  surface,  where  sheltered  from 
the  waves,  and  also  at  considerable  depths,  out  of  material 
washed  off  the  land  by  the  waves  or  currents  ;  but  not 
making  coarse  sandy  or  pebbly  deposits  over  the  deep  bed 
of  the  ocean,  as  even  great  rivers  carry  only  silt  to  the 
ocean;  and  not  making  even  argillaceous  deposits  over  the 
ocean's  bed  except  along  the  borders  of  the  land,  unless 
by  the  aid  of  a  very  great  river  like  the  Amazon,  though 
even  in  that  case  the  greater  part  of  the  detritus  is  thrown 
back  on  the  .coast  by  the  waves  and  currents.     In  former 
geological  periods,  the  submerged  borders  of  the  conti- 
nents, on  which  sedimentation  mainly  takes  place,  were 
much  more  extensive  than  at  present. 

(2)  Through  living  species,  and  mainly  Mollusks,  Mol- 
luscoids,  Crinoids,  Corals,  and  Rhizopods,  affording  cal- 
careous material  for  strata;  and  Diatoms,  Radiolarians, 
and  Sponges,  affording  siliceous  material.  Most  rocks 
made  of  Corals  and  the  shells  of  Mollusks  have  required 
the  help  of  the  waves,  at  least  to  fill  up  the  interstices. 

2.  By  the  Waters  of  Lakes.  —  Lacustrine  deposits  are 
essentially  like  those  of  the  ocean  in  mode  of  origin,  unless 
the  lakes  are  small,  when  they  are  like  those  of  rivers. 

3.  By  the   Running  Waters  of  the  Land.  —  (1)  Filling 
the  valleys  with  alluvial  deposits,  and  moving  the  earth 
from  the  hills  over  the  plains  (page  138).      (2)  Carrying 
detritus  to  the  sea  or  to  lakes,  to  make,  in  conjunction 


HEAT.  167 

with  the  action  of  the  waters  of  sea  or  lake,  deltas  and 
other  shore  accumulations  (pages  138,  153). 

4.  By  Frozen  Waters.  —  (1)  Acting  in  the  condition  of 
glaciers ;  and  thus  spreading  the  rocks  and  earth  of  the 
higher  lands  over  the  lower,  in  definite  lines  of  moraine, 
or  in  sheets  of  drift,  bearing  onward  in  the  process,  blocks 
of  great  size,  as  well  as  finer  material*  (page  162). 
(2)  Acting  as  icebergs ;  and,  in  this  condition,  transport- 
ing stones  and  earth  to  distant  parts  of  the  ocean,  as 
from  the  Arctic  regions  to  the  Newfoundland  Banks,  and 
so  contributing  to  sedimentary  accumulations  in  deep  or 
shallow  water,  distinguished  by  their  containing  huge 
blocks  of  stone,  besides  pebbles  and  earth. 

V.    HEAT. 
1.    Sources  of  Heat. 

The  crust  of  the  earth  derives  heat  from  three  sources : 
— >  1,  The  Sun,  an  external  source  ;  2,  The  Earth's  Heated 
Interior ;  3,  Chemical  and  Mechanical  Action. 

1.  The  Sun.  —  This  agency  is  peculiar  in  being  regu- 
larly variable,  through  the  alternations  in  day  and  night, 
in  the  seasons,  in  the  time  of  aphelion  and  perihelion,  and 
in  the  eccentricity  of  the  earth's  orbit.  The  amount  of 
heat  imparted  to  the  earth  and  retained  by  it,  varies  also 
with  changes  in  the  atmosphere  ;  since  the  atmosphere 
absorbs  a  part  of  the  heat  radiated  to  the  earth  from  the 
sun  and  stars,  and  absorbs  in  greater  proportion  the  heat 
rays  of  extremely  great  wave  length  radiated  from  the 
earth.  The  following  are  some  of  the  causes  to  which 
change  in  climate  has  been  attributed  :  — 

1.  A  gradual  diminution  in  the  heat  of  the  sun  through 
the  geological  ages.  Such  a  change  must  have  taken 
place ;  and  it  is  believed  by  Lord  Kelvin  and  others  that 
it  has  been  adequate  to  produce  a  very  considerable 
change  in  the  earth's  climate  since  the  beginning  of  Paleo- 
zoic time. 


168  DYNAMICAL  GEOLOGY. 

2.  Variations  in  the  condition  of  the  surface  of  the  sun, 
causing  periodical  alterations  in  the  amount  of  heat  radi- 
ated, and  thus  producing  alternating  cold  and  warm  eras. 
Such  changes  are  possible,  though  their  occurrence  has 
not  been  proved. 

3.  Variations  in. the  level  of  the  earth's  surface.     In 
any  latitude  the  highlands  are  colder  than  the  lowlands,  so 
that  very  appreciable  changes  of  climate  must  have  been 
produced  by  the  great  mountain  elevations  of  the  Tertiary 
era,  and  by  the  extensive  changes  of  continental  levels  in 
the  Quaternary.     But  even  more  important  may  be  the 
indirect  effects  of  crustal  movements,  when  a  change  in 
the  level  of  the  land  or  sea  bottom  diverts  the  oceanic 
currents  from  one  course  to  another.     Elevating  the  sea 
bottom  between  Europe  and  Greenland,  would  shut  out 
the  warm  Gulf  Stream  from  the  Arctic  region,  and  in- 
crease its  cold.      For,  according   to  Croll's  calculations, 
this  stream  contributes  to  the  North  Atlantic  Ocean  77,- 
479,650,000,000,000,000  foot-pounds  of  energy,  in  the  form 
of  heat,  per  day.     Such  a  change  might,  therefore,  make 
a  glacial  climate  for  large  areas  in  the  northern  hemi- 
sphere.    On  the  contrary,  a  subsidence  opening  Bering 
Strait  for  the  free  passage  of  the  tropical  current  of  the 
Pacific  would  ameliorate  the  Arctic  climate. 

4.  Variations  in  the  constitution  of  the  earth's  atmos- 
phere.    As  already  stated,  the  atmosphere  absorbs  a  part 
of  the  heat  radiated  from  the  sun  to  the  earth,  but  absorbs 
in  greater  proportion  the  heat  rays  of  very  great  wave 
length  emitted  from  the  earth.     The  effect  of  the  atmos- 
phere is  to  make  the  temperature  of  the  surface  of  the 
earth  more  uniform,  and  on  the  average  higher,  than  it 
would  otherwise  be.    This  absorptive  action  is  chiefly  due 
to  the  carbon  dioxide  and  water  vapor  in  the  atmosphere. 
It  has  been  inferred  that  the  effect  of  a  larger  amount  of 
these   constituents    (which    must  have   existed   in   early 
geological   time)   would   have   been   to   make   the   earth 
warmer   than   at   present.     The    researches   of    Langley, 


HEAT.  1169 

however,  have  shown  that  the  law  of  selective  absorption 
of  heat  rays  by  the  atmosphere  is  more  complex  than  was 
formerly  supposed ;  and  the  inference  as  to  the  climatic 
effect  of  the  greater  amount  of  water  vapor  and  carbon 
dioxide  in  former  times,  is  somewhat  doubtful. 

5.  Variations  in  the  eccentricity  of  the  earth's  orbit. 
The  earth,  through  all  such  variations,  receives  the  same 
amount  of  heat  annually  from  the  sun,  but  not  the  same 
for  the  winter  as  for  the  summer.  The  maxima  of  eccen- 
tricity are  unequal,  and  are  passed  at  variable  periods 
ranging  from  about  100,000  to  somewhat  more  than 
200,000  years.  The  earth  is  at  present  near  a  minimum, 
and  the  distance  from  the  sun  is  about  93.9  millions  of 
miles  in  aphelion  (which  comes  now  in  summer),  and 
nearly  90.9  millions  in  perihelion  —  the  difference,  about 
3  millions.  About  100,000  years  since,  a  maximum  oc- 
curred, with  the  aphelion  and  perihelion  distances  96.65 
and  88.15  millions  of  miles  —  the  difference,  8J  millions; 
and  850,000  years  since,  an  extreme  maximum,  with  these 
distances  99.3  and  85.5  millions  —  the  difference,  13.8 
millions  of  miles.  When  the  aphelion  comes  in  the  winter 
of  the  northern  hemisphere,  the  cold  of  the  winters  in  that 
hemisphere  is  increased,  the  amount  of  heat  received  being 
inversely  as  the  square  of  the  distance  (which  ratio  gives 
for  the  heat  in  winter,  during  the  extreme  maximum  re- 
ferred to,  about  five  sixths  of  that  now  received  in  that 
season).  Moreover,  the  winter  part  of  the  year  (from 
the  autumnal  to  the  vernal  equinox)  is,  at  the  extreme 
maximum,  36  days  longer  than  the  summer  part  (from 
the  vernal  to  the  autumnal  equinox) ;  whereas  at  present 
the  latter  is  8  days  the  longer.  At  the  same  time,  the 
summers  are  hotter,  but  shorter.  In  the  southern  hemi- 
sphere the  reverse,  in  each  respect,  is  true.  The  cold 
of  a  Glacial  period  has  been  thus  accounted  for,  and  also 
the  warmth  of  warm  eras,  by  Croll;  but  others  reject 
the  theory.  The  theory  requires  several  Glacial  epochs  in 
each  hemisphere  during  one  prolonged  time  of  maximum 


170  DYNAMICAL   GEOLOGY. 

eccentricity,  since  the  effect  of  precession  and  revolution 
of  the  apsides  is  to  reverse  the  relation  of  the  seasons  of 
each  hemisphere  to  aphelion  and  perihelion  twice  in  a 
cycle  of  about  21,000  years.  In  an  age  of  maximum 
eccentricity,  Glacial  epochs  should  accordingly  occur  alter- 
nately in  the  northern  and  the  southern  hemisphere,  cul- 
minating at  intervals  of  10,500  years. 

6.  A  change  in  the  earth's  axis  has  been  suggested  as 
a  possible  cause  of  variation  in  climate.  But  calculations 
by  G.  H.  Darwin,  Haughton,  and  others,  have  shown  that 
no  such  change  can  have  taken  place  sufficient  for  any 
marked  result. 

2.  Internal  Heat.  —  The  fact  of  a  high  temperature  in 
the  earth's  interior  is  established  in  various  ways. 

1.  The  form  of  the  earth  is  a  spheroid,  and  a  spheroid 
of  just  the  shape  that  would  have  resulted  from  the  earth's 
revolution  on  its  axis,  provided  it  had  passed  through  a 
state  of  fusion,  and  had  slowly  cooled  over  its  exterior. 
Hence  is  drawn  the  inference  that  it  has  passed  through 
such  a  state  of  fusion,  which  is  strengthened  by  the  other 
evidence  here  given.     Another  conclusion  also  follows ; 
namely,  that  the  earth's  axis  had  the  same  position  (or,  at 
least,  very  nearly  the  same)  when  cooling  began  as  now. 
There  is  no  evidence  that  there  has  been  at  any  time  any 
considerable  change. 

2.  In  deep  borings  for  water,  and  in  shafts  sunk  in 
mining,  it  has  been  found  that  the  temperature  of  the 
earth's  crust  increases,  on  an  average,  one  degree  Fahren- 
heit for  55  to  60  feet  of  descent.     Such  a  rate,  in  the 
latitude  of  New  York,  would  give  heat  enough  to  boil 
water  at  a  depth  of  less  than  two  miles ;  and  at  a  depth 
of  35  miles  the  temperature  would  be  3000°  F.,  or  that  of 
the  fusing  point  of  iron.     Since,  however,  the  fusing  tem- 
perature of  nearly  all  substances  increases  with  the  pres- 
sure, a  zone  of  universal  fusion  in  the  earth,  if  such  a  zone 
exists  at  all,  must  be  at  a  much  greater  depth  than  would 
be  suggested  by  the  figures  given  above. 


HEAT.  171 

3.  The  great  Pacific  Ocean  has  nearly  a  complete  girdle 
of  volcanoes,  extinct  or  active  ;  and  all  of  its  many  islands 
that  are  not  coral  islands,  are  volcanic,  excepting  New 
Zealand  and  a  few  others  of  large  size  in  its  southwest 
part.      Volcanoes  occur  along  many  parts  of  the  Andes 
from  Tierra  del  Fuego  to  the  Isthmus  of  Darien ;  in  Cen- 
tral America,  in  Mexico,  California,  Oregon,  and  beyond  ; 
in  the   Aleutian    Islands  on  the  north ;    in   Kamchatka, 
Japan,  the  Philippines,  New  Guinea,  New  Hebrides,  and 
New  Zealand  on  the  west ;  and  in  Antarctic  lands  south 
of  New  Zealand  and  South  America.     The  volcanic  region 
thus  bounded  is  almost  a  hemisphere  ;  and,  besides,  there 
are   volcanoes  in  many  parts  of   the   other   hemisphere. 
Outlets  of  molten  matter  so  extensively  distributed  seem 
to  indicate  that  there  is  some  world- wide  region  of  heat 
beneath. 

4.  The  flexures  which  the  earth's  crust  and  its  strata 
have  undergone  over  regions  of  continental  extent,  and 
even  as  late  as  the   Cenozoic,  have  been  held  by  some 
to  prove  that  there  have  been,  up  to  the  middle  Cenozoic, 
if   not  later,  great   regions  of   liquid    rock   beneath   the 
earth's  crust;  though  most  physicists  and  geologists  be- 
lieve those  movements  to  be  compatible  with  a  condition 
of  substantial  solidity  of  the  globe. 

3.  Chemical  and  Mechanical  Action.  —  In  the  upturning 
and  flexure  of  rocks  attending  mountain-making,  there 
have  been  movements  on  a  grand  scale  ;  and,  through  the 
transformation  of  this  motion  into  heat,  the  rocks  have 
received  in  some  cases  a  high  temperature,  sufficient  to 
promote,  through  the  moisture  present,  the  consolidation 
of  rocks,  and  even  their  crystallization,  or  metamorphism  ; 
and  also,  in  the  view  of  Mallet,  their  fusion  on  a  scale 
grand  enough  to  originate  volcanoes.  This  is  probably 
one  chief  source  of  the  heat  through  which  the  metamor- 
phism and  consolidation  of  rocks  have  been  produced,  the 
other  chief  source  being  the  internal  heat. 

Heat   is   produced    by   condensation,    as    when   vapors 


172  DYNAMICAL   GEOLOGY. 

become  liquid  or  solid,  or  when  liquids  (as  water)  become 
solid.  It  is  also  produced  in  many  chemical  changes, 
as  in  the  oxidation  of  pyrite  and  other  substances. 

2.    Effects   of    Heat. 

The  following  are  the  effects  of  heat  here  considered:  — 
1,  Expansion  and  Contraction;  2,  Eruptions  of  Igneous  Rock, 
and  associated  phenomena ;  3,  Metamorphism ;   4,  Forma- 
tion of  Veins. 

The  subject  of  movements  of  the  earth's  crust,  and 
the  evolution  of  continents  and  mountain  ranges,  might 
be  included  here,  since  these  movements  probably  result 
from  the  reaction  of  the  earth's  heated  interior  upon  its 
surface ;  but  the  subject  is  so  comprehensive  that  it  has 
been  deemed  best  to  give  it  a  distinct  chapter  (page  203). 

1.    EXPANSION  AND  CONTRACTION. 

(1)  Heat  from  any  subterranean  source  penetrating 
upward  may  cause  wide  changes  of  level.  Lyell  has  cal- 
culated that  a  mass  of  sandstone  a  mile  thick,  raised 
in  temperature  to  1000°  F.,  would  have  its  upper  surface 
elevated  50  feet.  Fractures  and  displacements  would  be 
likely  to  attend  such  movements.  (2)  The  diurnal  varia- 
tion of  temperature,  which  in  some  countries  amounts  to 
80°  F.  or  more,  and  also  the  annual  variation,  is  a  force 
always  at  work.  The  expansion  and  contraction  may 
gradually  move  blocks  of  rock  from  their  places.  It  will 
move  the  heated  side  of  the  block  outward ;  and,  if  this 
outer  part  so  moved  cannot,  because  of  wedging  or  fric- 
tion, return  with  the  succeeding  contraction,  the  mass 
will  move  to  it  or  have  its  edges  fractured.  Blocks  lying 
on  a  slope  will  tend  to  crawl  downward,  since  gravitation 
will  make  the  downward  movement  slightly  exceed  the 
upward,  in  both  expansion  and  contraction.  The  Bunker 
Hill  obelisk  at  Charlestown  in  Massachusetts  has  been 
proved  to  swing  back  and  forth  with  the  passage  of  the 
sun  over  it.  (3)  The  alternating  action  of  expansion  and 


HEAT. 


173 


FIG.  198. 


contraction  peels  off  the  grains  or  outer  surface  of  rocks, 
and  is,  especially  in  dry  climates,  an  important  means  of 
rock  disintegration. 

Shrinkage  Cracks.  —  (1)  In  the  cooling  of  liquid  rocks 
shrinkage  cracks  are  produced, 
and  thence  comes  the  columnar 
structure  of  trap,  basalt,  etc. 
(Fig..  193).  The  columns  show 
a  tendency  to  the  form  of  hex- 
agonal prisms,  since  less  expen- 
diture of  force  in  the  rupture 
of  cohesion  is  required  to  pro- 
duce a  hexagonal  network  of 
cracks  than  one  of  any  other 
form.  The  cracks  tend  to  be  propagated  in  a  direction 
perpendicular  to  the  cooling  surface  ;  and  the  position 
of  the  columns  is  thereby  determined.  Fingal's  Cave 


Columnar  structure. 


FIG.  194. 


Basaltic  columns,  Illawarra,  New  South  Wales. 

and  the  Giant's  Causeway  are  familiar  examples  of  co- 
lumnar structure  in  great  perfection.  Fig.  194  (from 
a  sketch  by  the  author  in  1840)  illustrates  the  same 
phenomenon  at  Illawarra  on  the  coast  of  New  South 
Wales.  (2)  Similar  columnar  forms  are  sometimes  pro- 
duced in  sandstone  after  heating,  though  in  general  only 
irregular  cracks  result.  (3)  Heat  penetrates  rocks  over 


174  DYNAMICAL  GEOLOGY. 

wide  regions  wherever  metamorphism  is  in  progress ;  and 
the  subsequent  cooling  and  contraction  may  leave  multi- 
tudes of  fractures,  in  long  lines  or  in  reticulations,  the 
subsequent  filling  of  which  may  make  veins. 

Drying  is  another  source  of  shrinkage  cracks.  It  makes 
the  shallow  mud-cracks  (page  156),  and  the  soil-cracks, 
sometimes  yards  in  depth,  in  countries  of  fertile  prairies 
that  have  a  long  hot  and  dry  season ;  and  may  produce 
far  deeper  jointlike  cracks  in  mud-made  rocks  (shales 
and  argillaceous  sandstones),  as  they  become  slowly  dried 
by  the  action  of  subterranean  heat.  Further,  the  drying 
of  beds  produces  a  sinking  of  the  surface.  A  soft  mud 
may  contract  to  a  tenth  of  its  bulk.  All  mud  beds  will 
suffer  a  large  diminution  in  thickness  on  drying ;  but  the 
pressure  of  overlying  strata  may  prevent  shrinkage  cracks 
from  forming. 


2.    ERUPTIONS  OF  IGNEOUS  ROCK,  AND  ASSOCIATED  PHENOMENA. 
GENERAL  NATURE  OF  VOLCANOES  AND  THEIR  PRODUCTS. 

Volcanoes  are  mountain  elevations  of  a  somewhat  coni- 
cal form,  which  have  a  crater  at  the  summit,  and  eject, 
from  time  to  time,  vapors  and  melted  rock.  If  the  ejec- 
tions have  long  since  ceased,  the  volcano  is  said  to  be 
extinct. 

The  cavity  or  pit  in  the  top  of  a  volcanic  mountain, 
called  the  crater,  where  the  lavas  may  often  be  seen  in 
fusion,  is  sometimes  thousands  of  feet  deep,  but  may  be 
quite  shallow  ;  and  in  extinct  volcanoes  it  is  often  wholly 
wanting,  owing  to  its  having  been  left  filled  when  the 
action  ceased. 

The  liquid  rock  issuing  from  a  crater,  and  the  same 
after  becoming  cold  and  solid,  is  called  lava. 

An  active  crater,  even  in  its  most  quiet  state,  emits 
vapors.  These  vapors  are  mostly  steam,  or  aqueous  vapor; 
but  in  addition  there  are  usually  sulphur  gases,  and  some- 


HEAT.  175 

times  carbonic  acid,  hydrochloric  acid,  and  more  rarely 
other  gases. 

In  a  time  of  special  activity  fiery  jets  are  sometimes 
thrown  up  to  a  great  height,  which  are  made  of  red-hot 
fragments  —  the  fragments  of  great  bubbles  of  lava  pro- 
duced by  the  escaping  vapors.  The  fragments  cool  as 
they  descend  about  the  sides  of  the  crater,  and  are  then 
called  cinders  or  ashes,  according  as  they  are  coarse  or  fine. 

When  a  shower  of  rain  (which  often  results  from  the 
condensation  of  the  escaping  steam)  accompanies  the  fall 
of  the  ashes,  the  result  is  a  mudlike  mass,  which  becomes, 
on  drying,  a  brownish  or  yellowish  brown  rock  called  tufa. 
Tufa  is  often  much  like  a  soft  sandstone,  except  that  the 
materials  are  of  volcanic  origin. 

The  materials  produced  by  the  volcano  are,  then :  — 
1,  Lavas ;  2,  Cinders  and  ashes;  3,  Tufas;  4,  Vapors  or 
gases. 

The  lavas  are  of  various  kinds.  They  are  often  more 
or  less  cellular  —  sometimes  light  cellular,  like  the  scoria 
of  a  furnace,  —  but  more  commonly  heavy  rocks,  with  some 
scattered  ragged  cellules  or  cavities  through  the  mass.  A 
stream  of  lava  of  this  more  solid  kind  has  often  a  few 
inches  of  scoria  at  top,  as  a  running  stream  of  sirup  may 
have  its  scum  or  froth.  The  most  of  the  scoria  has  this 
scum-like  origin.  Pumice  is  a  very  light  grayish  scoria, 
full  of  long  and  slender  parallel  air  cells. 

When  lava  cools  rapidly,  it  solidifies  as  a  glass — ob- 
sidian or  tachylite  (pages  38,  39).  When  it  cools  slowly, 
it  forms  a  truly  crystalline  rock.  Between  the  extremes 
are  various  gradations. 

The  stony,  or  crystalline,  lavas  may  be  divided  into 
three  groups,  according  to  their  chemical  and  mineralogi- 
cal  constitution,  of  which  basalt,  andesite,  and  trachyte 
may  be  considered  types.  The  lavas  of  the  first  group 
consist  chiefly  of  pyroxene  and  labradorite.  They  contain 
a  relatively  small  amount  of  silica,  are  dark  and  heavy 
rocks  (specific  gravity  above  2.8),  and  have  an  average 


176 


DYNAMICAL   GEOLOGY. 


fusion  point  of  about  2250°  F.  Those  of  the  second  group 
consist  chiefly  of  hornblende  (or  pyroxene)  and  oligoclase 
or  andesine.  In  percentage  of  silica,  specific  gravity,  and 
fusibility,  they  hold  an  intermediate  position.  Their  aver- 
age fusion  point  is  about  2520°  F.  Those  of  the  third 
group  consist  chiefly  of  orthoclase,  and  sometimes  contain 
some  quartz.  They  have  a  high  percentage  of  silica,  and 
a  specific  gravity  below  2.7.  They  are  often  light-colored. 
Their  fusion  point  is  about  2700°  F.,  and  some  of  them  are 
considerably  viscid  even  at  a  temperature  of  3100°  F. 

FIG.  195. 


Mount  Vesuvius:  from  a  sketch  by  the  author  in  June,  1834.  —a,  the  main  cone;  &, 
summit  cinder  cone ;  c,  Monte  Somma,  part  of  former  outline  of  crater ;  d,  Hermitage 
(now  Observatory) ;  e,ft  Portici  and  Kesina,  covering  the  site  of  Herculaneum  ;  g,  Torre 
del  Greco. 

A  volcanic  mountain  is  made  out  of  the  ejected  mate- 
rials :  either  —  (1)  of  lavas  alone;  (2)  of  cinders  alone; 
(3)  of  tufas  alone ;  or  (4)  of  alternations  of  two  or  more 
of  these  materials.  As  the  ejections  flow  off  or  fall  more 
or  less  symmetrically  around  the  vent,  the  form  of  a  vol- 
canic peak  necessarily  tends  to  become  conical. 

The  angle  of  slope  of  a  lava  cone  is  from  3°  to  10°  ;  of  a 
tufa  cone,  15°  to  30°;  of  a  cinder  cone,  30°  to  42°;  of  mixed 
cones,  intermediate  inclinations  according  to  their  consti- 
tution. 


HEAT. 


177 


The  cone  of  Vesuvius,  shown  in  Fig.  195,  consists 
mostly  of  cinders,  and  is  accordingly  pretty  steep.  Etna, 
about  10,000  feet  high,  and  Mauna  Loa  in  Hawaii,  nearly 
14,000  feet,  consisting  mainly  of  lava  streams,  have  an 
average  slope  of  less  than  10°.  The  form  of  a  cone  with 
a  slope  of  7°  —  which  is  the  average  for  the  Hawaiian 
volcanoes — is  shown  in  Figs.  196,  197.  Fig.  196  has  a 
pointed  top  like  Mauna  Kea,  and  Fig.  197  a  rounded  out- 

FIG.  196. 


Mauna  Kea. 

line  like  Mauna  Loa,  whose  form  is  that  of  a  very  low 
dome. 

The  highest  of  volcanic  mountains  on  the  globe  are  the 
Aconcagua  peak  in  Chile,  23,000  feet,  and  Sorata  and 
Illimani  in  Bolivia,  each  over  24,000  feet.  .  The  former 
appears  to  be  still  emitting  vapors.  The  mountains 

FIG.  197. 


Mauna  Loa. 

Shasta,  Hood,  St.  Helen's,  and  others  in  California  and 
Oregon,  are  isolated  volcanic  cones  11,000  to  14,400  feet 
high,  the  latter  being  the  height  of  Mount  Shasta.  The 
average  slope  of  the  upper  half  of  Mount  Shasta  is  about 
27°.  The  slopes  of  most  of  the  lofty  volcanoes  of  the 
Andes  are  between  25°  and  34°. 


VOLCANIC  ERUPTIONS. 

The  process  of  eruption,  though  the  same  in  general 
method  in  all  volcanoes,  varies  much  in  its  phenomena. 
The  fundamental  principles  are  well  shown  at  the  great 
craters  of  Hawaii,  the  southeasternmost  of  the  Hawaiian 
(or  Sandwich)  Islands. 


178  DYNAMICAL   GEOLOGY. 

General  Description  of  Hawaii.  —  Hawaii  is  made  up 
mainly  of  three  volcanic  mountains  —  two,  Mauna  Kea 
and  Mauna  Loa  (Figs.  196,  197,  page  177),  nearly  14,000 
feet  high ;  and  one  (the  western),  Mauna  Hualalai,  about 
10,000  feet.  Mauna  Kea  is  alone  in  being  extinct. 

Mauna  Loa  has  a  great  crater  at  its  summit,  and 
another  independent  one  4000  feet  above  the  level  of 
the  sea.  The  latter  is  the  famous  Kilauea,  called  also 
Lua  PSle,  or  Pele's  pit,  Pele  being,  in  the  mythology  of 
the  Hawaiians,  the  goddess  of  the  volcano. 

The  accompanying  map  of  Hawaii  (Fig.  198)  shows 
the  positions  of  Mauna  Loa  and  Mauna  Kea,  and  of  the 
crater  of  Kilauea.  , 

Kilauea.  —  The  crater  of  Kilauea  is  literally  a  pit.  It 
is  three  miles  in  greatest  length,  and  nearly  two  in  great- 
est breadth,  and  about  seven  and  a  half  miles  in  circuit. 
The  pit  has  nearly  vertical  sides  of  solid  rock  (made 
of  lavas  piled  up  in  successive  layers),  and  has  been 
1000  feet  in  depth  after  several  of  its  eruptions,  and  400 
to  600  feet  previous  to  its  eruptions.  The  bottom  is  a 
great  area  of  solid  lava,  with  one  or  more  lakes  or  pools 
of  liquid  lava,  or  crater-like  openings,  from  which  vapors 
rise.  The  largest  lake,  in  1840,  was  1000  feet  in  diameter. 
The  interior  may  be  surveyed  from  the  brink  of  the  pit, 
even  when  in  most  violent  action,  as  calmly  and  safely  as 
if  the  landscape  were  one  of  houses  and  gardens. 

Action  in  Kilauea.  —  The  ordinary  action,  in  the  inter- 
vals between  the  great  eruptions,  is  simply  this.  The 
lavas  in  the  active  pools  are  in  a  state  of  ebullition,  jets 
rising  and  falling  as  in  a  pot  of  boiling  water  —  with  this 
difference,  that  the  jets  are  30  to  100  feet  high.  Such  jets, 
in  lava  as  well  as  water,  arise  from  the  effort  of  vapors  to 
escape  ;  in  water  the  vapor  is  steam  derived  from  the  water 
itself ;  in  lavas  it  is  chiefly  steam  from  waters  that  have 
gained  access  to  the  lavas,  but  also  gases  and  vapors  de- 
rived from  materials  in  the  lavas,  or  from  depths  below. 

The  lavas  of  the  pools  or  lakes  overflow  at  times  and 


HEAT. 


179 


spread  in  streams  across  the  great  plain  that  forms  the 
bottom  of  the  crater.  In  times  of  great  activity  the  pools 
and  lakes  are  numerous,  the  ebullition  incessant,  the  jets 


FIG.  193. 


HAWAII 

F.ROM  THE 

GOVERNMENT  MAP 

SCALE  OF  MILES 


higher,  and  the  overflowings  follow  one  another  in  quick 
succession. 

Cause  of  Eruption.  —  In  part  as  the  result  of  these  over- 
flows, but  in  part  (and  sometimes  chiefly)  as  the  result  of 
the  bodily  uplifting  of  the  crater  floor  by  lavas  ascending 
beneath  it,  the  pit  slowly  fills.  In  the  intervals  between 


180  DYNAMICAL   GEOLOGY. 

1823  and  1832,  and  between  1832  and  1840,  the  bottom 
was  raised  400  feet  or  more  above  the  lowest  level,  so  that 
the  depth  was  reduced  from  1000  feet  to  600  feet  or  less. 
The  addition  of  400  feet  to  the  height  of  the  column  of 
liquid  lava  in  the  crater  caused  a  corresponding  increase 
of  pressure  against  the  sides  of  the  mountain.  The  amount 
of  this  pressure  is  at  least  two  and  a  half  times  as  great 
as  that  which  a  column  of  water  of  equal  height  would 
produce.  The  mountain  must  be  strong  to  bear  it.  The 
lavas  at  such  times  may  be  in  a  state  of  violent  activity, 
and  a  large  addition  to  the  pressure  against  the  sides  of 
the  mountain  comes  from  the  force  of  the  imprisoned 
vapors. 

The  consequence  of  this  increase  of  pressure,  both  from 
the  lavas  and  the  vapors,  may  be,  and  has  several  times 
been,  a  breaking  of  the  sides  of  the  mountain.  One  or 
more  fractures  result,  and  out  flows  the  lava  through  the 
openings.  Thus  simple  have  been  the  eruptions. 

In  the  eruption  of  1840  the  lavas  first  appeared  at  the 
surface  a  few  miles  below  Kilauea,  and  then  again  at  other 
points  somewhat  more  remote ;  finally  a  stream  (repre- 
sented on  the  map,  Fig.  198)  began  at  a  point  about  15 
miles  east  of  the  great  crater,  and  extended  to  the  shores 
at  Nanawale.  Here,  on  encountering  the  waters,  the  great 
flood  of  lava  was  shivered  into  fragments,  and  the  whole 
heavens  were  thick  with  an  illuminated  cloud  of  vapors 
and  cinders,  the  light  coming  from  the  fiery  stream  below. 
The  lavas  which  escaped  at  this  relatively  small  eruption 
amounted  to  at  least  15,400,000,000  cubic  feet. 

This  eruption  of  Kilauea  took  place,  it  will  be  observed, 
not  over  the  sides  of  the  crater,  but  through  breaks  in  the 
mountain's  sides  below ;  and  the  pressure  of  the  column 
of  lava  within,  and  that  of  the  escaping  vapors,  appear  to 
have  caused  the  break. 

Summit  Crater  of  Mauna  Loa.  —  Eruptions  have  also 
taken  place  from  the  summit  crater  of  the  same  mountain 
(Mauna  Loa),  which  is  nearly  14,000  feet  above  the  sea ; 


HEAT.  181 

and  in  each  case  there  has  been,  not  an  overflow  from  the 
crater,  but  an  outflow  through  breaks  in  the  sides  of  the 
mountain.  In  1852  there  was  first  a  small  issue  of  lavas 
near  the  summit,  and  then  another  of  great  magnitude 
about  10,000  feet  above  the  sea  level.  At  this  second 
outbreak  the  lava  was  thrown  up  in  a  fountain,  or  mass  of 
jets,  two  or  three  hundred  feet  high  ;  and  thus  it  continued 
in  action  for  several  days.  The  forms  of  the  fountain  of 
liquid  fire  were  compared  by  Rev.  T.  Coaii  to  the  clustered 
spires  of  a  Gothic  cathedral.  Similar  lava  fountains  have 
been  observed  also  at  other  eruptions  of  the  volcano. 

The  pressure  producing  the  jet  in  the  case  above  men- 
tioned, so  far  as  it  was  hydrostatic,  was  that  of  the  column 
of  lava  between  the  point  of  outbreak  and  the  level  of  the 
lavas  in  the  summit  crater,  3000  to  4000  feet  above.  The 
same  pressure  in  connection  with  confined  vapors  must 
have  caused  the  breaking  of  the  mountain  in  which  the 
eruption  began. 

Usually,  no  great  earthquakes  accompany  the  Hawaiian 
eruptions,  sometimes  not  even  slight  ones,  the  first  an- 
nouncement being  merely  "a  light  on  the  mountain." 
But  the  eruptions  of  1868  and  1887,  from  the  summit 
crater  of  Mauna  Loa,  were  preceded  by  earthquakes  of 
considerable  violence.  When  the  summit  crater  is  in 
action,  Kilauea,  though  10,000  feet  lower  on  the  same 
mountain,  and  even  a  larger  pit  crater,  commonly  shows 
no  agitation,  no  signs  whatever  of  sympathy. 

At  some  of  the  eruptions  of  Mauna  Loa  the  lava  has 
continued  down  the  mountain  to  a  distance  of  50  or  60 
miles. 

The  shaded  bands  descending  from  near  the  summit,  on 
the  map  (Fig.  198),  show  the  courses  of  several  great  out- 
flows of  lava. 

Conclusions.  —  These  cases  of  eruption  indicate  (1) 
that  the  lavas  go  on  gradually  increasing  the  pressure 
in  the  interior  by  their  accumulation,  while  augmented 
activity  in  the  production  of  vapors  still  further  increases 


182  DYNAMICAL   GEOLOGY. 

the  pressure ;  and  that  finally  the  mountain,  when  it  can 
no  longer  resist  the  forces  within,  somewhere  breaks  and 
lets  the  heavy  liquid  out.  They  show  (2)  that,  while 
earthquakes  may  attend  volcanic  action,  they  are  no  neces- 
sary part  of  it.  They  show  (3)  that  lavas  may  be  so  very 
liquid  that  no  cinders  are  formed  during  a  great  erup- 
tion ;  for,  in  the  ebullition  of  the  lava  in  the  boiling  lakes 
of  Kilauea,  the  jets  (made  by  the  confined  vapors)  are 
usually  thrown  only  to  a  height  of  30  to  100  feet ;  and,  on 
falling  back,  the  material  is  still  hot ;  it  either  falls  back 
into  the  pool  or  lake,  or  becomes  plastered  to  its  sides. 
The  liquidity  of  the  lavas  is  shown  by  the  jetting  out 
sometimes,  from  small  holes,  of  drops  but  a  fourth  of  an 
inch  thick,  which  fall  back  on  one  another,  adhere,  and  so 
make  a  model  of  a  fountain. 

Vesuvius.  —  Vesuvius  is  an  example  of  another  type 
of  volcano.  The  characteristic  of  the  Hawaiian  type  of 
volcanoes  is  the  comparatively  perfect  liquidity  of  the 
lavas.  The  lavas  are  of  the  most  fusible  (basaltic)  type  ; 
and  the  temperature  is  so  high  that  they  are  completely 
fused.  In  the  case  of  less  fusible  lavas,  the  temperature 
is  generally  insufficient  for  perfect  liquefaction,  sufficing 
only  to  bring  them  to  a  viscid,  semifused  condition.  In 
Vesuvius,  the  lavas  are  so  viscid  that  jets  cannot  rise 
freely  over  the  surface  :  the  vapors  are  therefore  kept 
confined  until  they  form  a  bubble  of  great  dimensions ; 
and,  when  such  a  bubble,  or  a  collection  of  them,  bursts, 
the  fragments  are  sometimes  thrown  to  a  height  of  thou- 
sands of  feet.  The  crater,  at  a  time  of  eruption,  is  a 
scene  of  violent  activity,  and  cannot  be  approached. 
Destructive  earthquakes  often  attend  the  eruptions. 

In  many  of  the  eruptions  of  Vesuvius,  there  has  been 
no  outflow  of  lava  streams,  the  lava  emitted  being  all  pro- 
jected into  the  air  by  the  violence  of  the  explosions,  and 
falling  as  cinders,  ashes,  or  tufa.  This  appears  to  have 
been  the  case  in  the  famous  eruption  in  the  year  79,  in 
which  Pompeii  and  Herculaneum  were  overwhelmed. 


HEAT.  183 

Before  that  catastrophe,  there  was  a  large  circular  crater, 
the  northern  half  of  whose  inclosing  rampart  remains  as 
the  ridge  of  Monte  Somma  (<?,  Fig.  195).  In  the  explo- 
sions of  that  eruption,  the  southern  half  of  the  old  ram- 
part disappeared. 

In  the  minor  activity  of  the  mountain,  during  the  inter- 
vals between  the  great  eruptions,  the  same  explosive  char- 
acter shows  itself.  Instead  of  quiet  outflows  from  lakes 
of  lava,  as  in  Kilauea,  there  are  generally  explosive  dis- 
charges of  cinders,  building  up  small  cones.  Such  a  cone 
is  shown  at  b  in  Fig.  195. 

The  lavas  at  Vesuvius  may  flow  directly  from  the  top 
of  the  crater ;  but  they  generally  escape  partly,  if  not 
entirely,  through  fissures  in  the  sides  of  the  mountain. 

Some  volcanoes,  as  those  of  Java,  are  characterized  even 
more  strongly  than  Vesuvius  by  the  predominance  of  the 
explosive  type  of  eruption.  The  eruption  of  Krakatoa  in 
1883  was  a  remarkable  example  of  this  type.  The  ashes, 
according  to  Verbeek,  ascended  to  a  height  of  more  than 
150,000  feet,  and  are  supposed  to  have  been  carried  around 
the  world,  and  to  have  caused  the  red  sunset  glows  of  the 
autumn  following.  Even  Kilauea  is  known  to  have  had 
one  violently  explosive  eruption,  probably  about  1789. 

Besides  the  difference  in  the  composition  of  the  lavas, 
other  circumstances,  as  the  size  of  the  conduit,  the  tem- 
perature of  the  subterranean  reservoir,  etc.,  affect  the 
character  of  the  eruption.  Such  extremely  violent  explo- 
sions as  that  of  Krakatoa  are  probably  due  to  the  sudden 
access  of  a  large  amount  of  water  to  the  molten  mass. 

Of  the  two  causes  of  eruption  —  hydrostatic  pressure, 
and  elastic  force  of  confined  vapors,  —  the  latter  appears 
to  be  the  most  effective  in  Vesuvius,  while  the  former  may 
be  in  Hawaii.  The  vapors  in  Mauna  Loa  appear  to  be 
supplied  mainly  by  the  fresh  waters  (rains)  which  fall 
over  the  mountain  and  descend  through  the  rocks ;  while 
Vesuvius  is,  in  part  at  least,  supplied  by  salt  waters  from 
the  Mediterranean,  as  is  proved  by  the  presence  of  hydro- 


184  DYNAMICAL   GEOLOGY. 

chloric  acid  in  its  vapors,  and  of  chlorides  among  its  saline 
incrustations. 

Trachytic  Domes.  —  Trachytic  lavas  are  less  common 
in  modern  volcanoes  than  the  basaltic.  They  have  in 
some  cases  preceded  basalt  in  the  history  of  a  volcanic 
cone.  In  some  cases  these  trachytic  lavas  (which,  owing 
to  the  predominance  of  orthoclase  in  their  constitution,  are 
much  less  fusible  than  the  basaltic)  have  come  up  through 
fissures  in  so  pasty  a  state  that  they  have  swelled  up  into 
steep  domes  and  cooled  in  this  form.  Domes  of  this  kind 
occur  in  Auvergne ;  also  in  the  Black  Hills  of  South 
Dakota  (Newton  and  Jenny). 

Lateral  Cones  of  Volcanoes.  —  In  eruptions  through  fis- 
sures the  lavas  may  continue  issuing  for  some  days  or 
weeks  through  the  widest  or  most  freely  open  part  of  the 
fissure,  and  consequently  form  at  this  point  a  cone  of  cin- 
ders or  lava.  Thus  have  originated  innumerable  cones 
on  the  slopes  of  Etna  and  other  volcanic  mountains. 

Submarine  Eruptions.  —  Eruptions  may  sometimes  take 
place  from  the  submarine  slopes  of  the  mountain  when 
it  is  situated  near  the  sea,  as  has  happened  with  Etna  and 
Mauna  Loa;  and  in  such  cases  accumulations  of  tufa  or 
of  solid  lava  may  form  under  water  about  the  opened  vent. 
The  numerous  volcanic  islands  of  the  ocean  of  course 
commenced  with  submarine  eruptions.  Fishes  and  other 
marine  animals  are  usually  destroyed  in  great  numbers  by 
such  submarine  eruptions. 

Subsidence  of  Volcanic  Regions ;  Overwhelming  of  Cities. 
—  Among  the  attendant  effects  of  volcanoes  are  the  sink- 
ing of  regions  in  their  vicinity  that  have  been  under- 
mined by  the  outflow  of 'the  lavas;  the  tumbling  in  of 
the  summit  of  a  mountain ;  and  earthquakes,  or  vibra- 
tions of  the  rocks,  in  consequence  of  fractures.  Another 
is  the  burial,  not  only  of  fields  and  forests,  but  even  of 
cities  and  their  inhabitants,  by  the  outflowing  streams,  or 
by  the  falling  cinders  and  accumulating  tufas.  Pompeii 
and  Herculaneum  are  two  of  the  cities  that  have  been 


HEAT.  185 

buried  by  Vesuvius ;  and  every  few  years  we  hear  of 
some  new  devastation  of  habitations  or  farms  by  this 
uneasy  volcano.  Pompeii  is  covered  only  by  the  tufas  of 
the  eruption  in  which  it  was  destroyed ;  Herculaneum  is 
covered  also  by  tufas  and  lava  streams  of  several  later 
eruptions. 

SUBORDINATE  VOLCANIC  PHENOMENA. 

1.  Solfataras.  —  In  the  vicinity  of  volcanoes,  and  some- 
times in  regions  in  which  no  active  volcanoes  exist,  there 
are  areas  where  steam,  sulphur  vapors,  and  perhaps  car- 
bonic acid  and  other  gases,  are  constantly  escaping.     Such 
areas  are  called  solfataras  (from  the  Italian,  solfo,  sulphur, 
and  terra,  earth).     The  sulphur  gases  deposit  sulphur  in 
crystals  or  incrustations  about  the  fumaroles  (as  the  steam 
holes  are  called) ;  and  alum  and  gypsum  often  form  from 
the  action  of  sulphuric  acid  (derived  from  the  oxidation 
of  the  sulphur  gases)  on  the  rocks. 

2.  Hot  Springs ;  Geysers.  —  Fountains  or  springs  of  hot 
water  are  common  in  volcanic  regions,  and  are  often  so 
abundant  as  to  be  used  for  baths.     Such  springs  occur 
also  in  many  other  parts  of  the  world,  especially  in  regions 
of  upturned  or  of  eruptive  rocks.     In  some  cases  the  heat 
is  produced  by  chemical  changes  in  progress  beneath,  or 
by  friction  and  crushing  of  rocks  in  the  upheavals  which 
have  taken  place  ;  but  often  the  source  is  the  residual  heat 
of  great  masses  of  lava. 

When  the  heated  waters  are  thrown  out  in  intermittent 
jets,  they  are  called  geysers.  The  Yellowstone  Park  in  the 
Rocky  Mountains  (between  the  parallels  of  44°  and  45°  N., 
and  the  meridians  of  110°  and  111°  W.)  is  the  most 
remarkable  region  of  geysers  in  the  world,  far  exceeding 
that  of  Iceland.  One  of  the  geysers  —  the  Beehive  — 
is  represented  in  action  in  Fig.  199.  The  Beehive  jet 
is  200  feet  high.  Its  eruptions  occur  at  somewhat  irreg- 
ular intervals,  but  generally  two  or  three  times  in  a  day. 
The  periods  of  other  geysers  vary  from  less  than  a  minute 


186 


DYNAMICAL  GEOLOGY. 


to  several  weeks.     The  eruptions  of  some  are  very  regu- 
larly periodical,  while  others  are  very  irregular. 

The  action  of  geysers  is  due  to  the  condition  that  sub- 
terranean waters  have  access  to  hot  rocks  (as  the  interior 


FIG.  199. 


Beehive  Ge,y 


HEAT.  187 

of  great  lava  sheets,  retaining  a  high  temperature  on 
account  of  the  poor  conductivity  of  the  material),  and' 
that  the  conduit  communicating  with  the  surface  is  so 
narrow  that  convection  currents  cannot  be  freely  estab- 
lished. The  heat  accordingly  increases  in  the  deeper  part 
of  the  column  of  water,  until  steam  is  formed,  by  whose 
expansion  the  cooler  waters  above  are  explosively  ejected. 
After  an  eruption,  the  water  flows  back  into  the  under- 
ground passages,  and  gradually  becomes  heated  up  for 
another  explosion. 

Heated  waters  act  on  the  rocks  with  which  they  are  in 
contact,  and  decompose  them  ;  and,  as  most  rocks  —  espe- 
cially volcanic  rocks  —  contain  some  kind  of  feldspar,  the 
waters  become  slightly  alkaline  through  the  alkali  of  the 
feldspar,  and  so  are  enabled  to  take  up  silica  and  make 
siliceous  solutions.  The  silica  taken  into  solution  is  de- 
posited again  around  the  geyser  in  many  beautiful  forms, 
and  makes  the  bowl  or  crater  from  which  the  waters  are 
thrown  out. 

When  the  material  in  the  vicinity  of  a  boiling  pool  con- 
sists of  earth  or  mud,  mud  cones  are  formed,  as  in  some 
parts  of  the  Yellowstone  Park,  and  also  at  Geyser  Canon, 
north  of  San  Francisco,  California. 

Besides  hot  springs  that  deposit  silica,  there  are  others 
that  deposit  calcium  carbonate,  making  thus  the  kind  of 
porous  limestone  called  travertine,  as  on  Gardiners  River, 
Yellowstone  Park. 

In  some  cases,  the  action  of  the  heated  waters  on  the 
rocks  exposed  to  them  gives  origin  to  deposits  of  quartz 
crystals,  agate,  opal,  and  different  silicates  and  other 
minerals. 

IGNEOUS  ERUPTIONS  NOT  VOLCANIC. 

It  has  been  stated  that  eruptions  of  volcanoes  generally 
take  place  through  fissures.  Fissure  eruptions  have  oc- 
curred also  in  regions  remote  from  volcanoes ;  and  they 
have  been  the  source  of  ejections  over  the  western  slope  of 


188  DYNAMICAL   GEOLOGY. 

the  Rocky  Mountains  vastly  greater  than  any  from  volcanic 
centers.  The  narrow  mass  of  igneous  rock  that  tills 
such  fissures  is  called  a  dike.  The  liquid  rock  has  some- 
times merely  filled  the  fissure,  without  overflowing ;  but 
in  other  cases  it  has  spread  widely  over  the  surface,  making 
sheets  of  great  extent  and  thickness.  The  outflow  of  liquid 
rock  has  often  been  followed  by  sedimentary  deposits,  and 
then  another  outflow  has  taken  place ;  thus  making  alter- 
nations of  fire-made  and  water-made  strata.  In  that  case, 
the  sheets  of  igneous  rock  are  said  to  be  contemporaneous, 
or  extrusive.  Beds  of  tufa,  or  "ash  beds,"  may  also  be 
included  in  the  series.  In  other  cases,  the  strata  have 
been  parted  along  a  plane  of  stratification,  and  molten 
rock  has  forced  itself  in.  Such  sheets  are  called  intrusive. 
In  the  case  of  intrusive  sheets,  both  the  overlying  and 
the  underlying  strata  are  affected  by  the  heat  of  the  igne- 
ous rock  (local  metamorphism,  page  190);  in  the  case  of 
contemporaneous  sheets,  only  the  underlying  strata. 

The  rocks  most  commonly  occurring  in  dikes  are  felsite, 
diorite,  and  dolerite  (pages  38,  39).  The  igneous  rock  is 
very  often  without  cellules  or  air  cavities ;  and,  if  any  are 
present,  they  are  in  general  neatly  formed,  instead  of 
being  ragged  like  those  of  lavas.  If  the  cavities  in  such 
a  rock  are  filled  by  the  deposit  of  minerals  (as  quartz,  cal- 
cite,  zeolites,  etc.),  it  is  called  amygdaloid.  The  rock  of 
an  amygdaloid  is  usually  hydrous  (and  chloritic)  through- 
out (owing,  it  is  supposed,  to  subterranean  waters  gaining 
access  in  some  way  while  the  eruption  was  in  progress); 
and  the  cavities  were  formed  in  the  outer  or  upper  part, 
where  the  diminished  pressure  allowed  of  the  water's  pass- 
ing to  the  state  of  vapor. 

Dikes  are  common  on  all  the  continents,  especially  in 
the  regions  between  the  summits  of  the  border  mountains 
and  the  ocean,  which  are  usually  between  300  and  800 
milss  in  breadth  ;  as,  for  example,  between  the  Appalach- 
ians and  the  Atlantic,  and  between  the  Rocky  Mountains 
and  the  Pacific. 


HEAT.  189 

The  Pacific  slope  of  the  Rocky  Mountains  (500  to  800 
miles  wide)  is  remarkable  for  its  lava  floods.  Some  of 
them  are  around  volcanoes,  or  volcanic  vents,  but  many 
were  from  fissure  eruptions  remote  from  any  volcano. 
The  largest  continuous  area  extends  from  the  Yellowstone 
Park  in  Wyoming,  westward  along  the  Snake  River 
through  southern  Idaho,  and  then  spreads  northward  over 
most  of  Oregon  and  a  large  part  of  Washington,  and 
southward  into  northern  California.  Its  boundaries  have 
not  been  exactly  determined,  but  its  area  is  estimated  to 
be  between  100,000  and  150,000  square  miles.  On  the 
western  margin  are  the  lofty  volcanoes  of  the  Cascade 
Range,  and  a  number  of  smaller  volcanoes  are  dotted  over 
various  parts  of  the  region ;  but  it  is  evident  that  these 
were  not  the  source  of  the  widespread  lavas.  The  Colum- 
bia River  is  bordered  for  long  distances  by  walls  1000  to 
2000  feet  high,  made  of  ranges  of  basaltic  columns ;  and, 
in  the  vicinity  of  Mount  Hood,  the  thickness  is  3500  feet. 
Again,  in  northern  California,  south  of  the  combined  vol- 
canic area  of  Mount  Shasta  and  Lassens  Peak,  on  the  west 
slope  of  the  Sierra,  the  lavas  were  so  copious  as  to  obliter- 
ate the  deep  valleys  of  an  old  system  of  drainage,  and 
force  the  streams  to  make  new  channels.  The  erosion 
then  begun  has  since  cut  out  valleys  1000  to  3000  feet 
deep,  partly  along  new  routes,  leaving  the  remnants  of  the 
lava  field  as  caps  of  "Table  Mountains."  The  miners 
have  tunneled  beneath  the  lava  cap  for  gold-bearing 
gravels,  and  found  rich  deposits  in  the  beds  of  the  old 
streams  (J.  D.  Whitney).  Nevada,  southern  Utah,  Colo- 
rado, New  Mexico,  and  Arizona  have  other  wide  lava  fields. 

Still  more  wonderful  are  the  fissure  eruptions  of  the 
Deccan,  in  India,  where  a  railway  out  of  Bombay  runs  for 
519  miles  continuously  over  a  lava  field ;  its  area  is  not 
less  than  200,000  square  miles. 

In  eastern  North  America,  outflows  through  fissures 
made  the  Palisades  on  the  Hudson  ;  long  narrow  ranges 
through  the  Connecticut  valley,  including  among  the  sum- 


190  DYNAMICAL  GEOLOGY. 

mits,  Mount  Tom  and  Mount  Holyoke ;  ridges  in  Nova 
Scotia ;  others  similar,  at  intervals,  from  New  Jersey  to 
North  Carolina;  and  others,  in  the  vicinity  of  Lake 
Superior.  In  Europe,  examples  are  seen  in  the  rocks  of 
Salisbury  Crags  near  Edinburgh,  and  of  the  Giant's  Cause- 
way and  FingaTs  Cave. 

The  intrusion  of  igneous  rock  has  at  times  lifted  the 
overlying  strata  high  enough  to  make  subterranean  dome- 
shaped  masses  1000  to  4000  feet  high  (named  laccoliths, 
from  the  Greek  Xa/c/eo?,  cistern,  and  Xt'0o9,  stone) ;  as  in  the 
Henry  Mountains,  in  southern  Utah,  where  denudation 
has  exposed  to  view  some  of  the  laccoliths  (G.  K.  Gilbert). 
Ten  thousand  feet  of  strata  are  said  to  have  been  thus 
lifted  —  evidence  of  the  vastness  of  the  erupting  force. 

3.  METAMORPHISM. 

The  term  metamorphism  signifies  change  or  alteration; 
and,  in  Geology,  specifically,  a  change  in  rocks,  under 
the  action  of  heat  and  other  subterranean  agencies  (but 
without  fusion),  generally  in  the  direction  of  greater 
induration  or  more  highly  crystalline  structure.  The 
rocks  which  have  suffered  such  a  change  are  probably  for 
the  most  part  ordinary  stratified  rocks,  mechanical  and 
organic.  But  lavas  and  other  igneous  rocks,  tufa  beds, 
and  chemical  deposits,  have  also  in  many  cases  undergone 
alteration  to  a  condition  in  which  they  are  undistinguish- 
able  from  metamorphosed  sediments.  Such  changes  may 
be  either  local  or  regional. 

Local  Metamorphism.  —  Local  metamorphism  has  often 
taken  place  in  the  walls  of  dikes  of  igneous  rocks,  or 
in  the  adjoining  parts  of  the  strata  over  or  between 
which  they  have  flowed,  in  consequence  of  the  heat  from 
the  melted  and  cooling  rock.  Near  dikes  of  trap,  the 
rock  is  sometimes  made  cellular  by  escaping  steam,  and 
filled  with  shrinkage  fissures  made  on  cooling  or  drying ; 
and,  besides  these  effects,  various  minerals  have  been 
often  formed,  as  epidote,  chlorite,  hematite,  tourmaline, 


HEAT.  191 

garnet,  out  of  the  ingredients  present  in  the  adjoining 
stratified  rock,  or  the  trap,  or  both.  The  waters  of  hot 
mineral  springs  have  often  produced  metamorphic  effects 
in  the  rocks,  and  many  mineral  species  have  been  formed 
by  this  means. 

Regional  Metamorphism.  —  In  regional  metamorphism, 
the  regions  undergoing  change  have  often  been  thou- 
sands of  square  miles  in  area,  and  the  depth  to  which 
the  alteration  has  extended  has  sometimes  exceeded 
30,000  feet.  The  rocks  were  originally,  in  great  part, 
uncrystalline  limestones,  shales,  sandstones,  conglomer- 
ates. They  are  changed  to  crystalline  limestone  or  marble, 
quartzite,  gneiss,  mica  schist,  and  the  like.  They  were 
originally  in  horizontal  strata ;  they  are  now  upturned 
or  folded,  and  are  often  intersected  by  veins. 

New  England  is  mostly  covered  by  metamorphic  rocks ; 
and  they  spread  over  the  eastern  border  of  New  York,  to 
Manhattan  Island.  They  occur  in  the  Adirondacks,  and 
over  a  large  area  in  Canada ;  in  the  Highlands  of  New 
Jersey  and  Putnam  County,  New  York;  in  the  Blue  Ridge 
and  the  Black  Mountains,  and  the  Piedmont  region  east  of 
those  mountains ;  in  a  large  area  south  of  Lake  Superior ; 
in  high  ranges  along  the  summit  of  the  Rocky  Mountains  ; 
and  in  the  Sierra  Nevada  in  California.  They  occur  also 
in  Scotland,  Wales,  Cornwall,  Scandinavia,  and  various 
other  regions. 

In  some  cases,  conclusive  proof  that  such  crystalline 
rocks  are  metamorphosed  stratified  rocks  is  afforded 
by  the  occurrence  of  unobliterated  fossils,  in  some  por- 
tions of  a  metamorphic  stratum,  where  the  change  is  least 
complete:  as  in  part  of  the  marble  of  West  Rutland  and 
other  places  in  Vermont ;  in  the  limestone  and  schists  near 
Poughkeepsie  and  elsewhere  in  Dutchess  County,  New 
York,  and  near  Bernardston,  Massachusetts  ;  in  the  Sierra 
Nevada  ;  in  Norway  ;  in  the  Alps  ;  and  in  several  other 
localities  in  Europe. 

In  other  cases,  a  sedimentary  origin  has  been  inferred 


192  DYNAMICAL  GEOLOGY. 

from  the  bedded  structure,  which  has  been  supposed  to 
correspond  to  the  original  stratification.  But  an  appear- 
ance of  bedding  is  by  no  means  conclusive  proof  of  the 
sedimentary  origin  of  a  rock.  Gneisses  and  allied  rocks 
are  undoubtedly  derived  in  some  cases  from  granites  and 
other  plutonic  rocks,  a  schistose  structure  being  devel- 
oped by  pressure  or  shearing.  When  the  planes  of  appar- 
ent bedding  in  gneisses  and  schists  are  parallel  to  the 
planes  of  contact  of  these  rocks  with  quartzites  or  crystal- 
line limestones,  the  probability  that  the  structure  represents 
a  true  stratification  is  strengthened.  While  the  presence 
of  a  schistose  structure  is  not  always  proof  of  origin  from 
sediments,  the  absence  of  such  structure  is  not  always 
proof  of  igneous  origin.  Granite  and  other  massive  rocks 
may  be  in  some  cases  only  the  extreme  term  of  metamor- 
phism  of  sediments.  It  is  not  always  possible  to  decide 
with  certainty  whether  a  mass  of  crystalline  rock  is  of 
igneous  or  of  sedimentary  origin. 

Effects.  —  The  effects  of  metamorphism  include:  — 

1.  Simple  compacting  and  solidification ;  as  in  making 
quartzite  from  quartzose  sandstone,  or  a  rock  looking  like 
granite  from  granitic  sandstone. 

2.  A  change  of  color;  as  the  gray  and  black  of  common 
limestone  to  the  white   color,  or  the  clouded  shadings, 
of  marble  ;  and  the  brown  and  yellowish  brown  of  some 
sandstones  colored  by  iron,  to  red,  making  red  sandstone 
and  jasper  rock. 

3.  In  most  cases,  a  partial  or  complete   expulsion   of 
water. 

4.  An  evolving  and  expulsion  of  mineral  oil  or  gas;  as 
when  bituminous  coal  is  changed  to  anthracite  or  graphite. 

5.  An  obliteration  of  all  fossils;  or  of  nearly  all,  if  the 
metamorphism  is  partial.     The  obliteration  is  usually  pre- 
ceded by  the  compression  and  distortion  of  the  fossils. 

6.  Often   a   change   in    crystallization,    with   little   or 
none  in  chemical  constitution ;    as  when  a  limestone  is 
turned  to  white  statuary  marble  ;    and   a   sandstone   or 


HEAT.  193 

argillaceous  rock,  made  from  the  disintegration  of  granite, 
gneiss,  and  related  rocks,  is  changed  to  granite  or  gneiss 
again.  Grains  of  pyroxene  may  be  changed  into  horn- 
blende, the  two  minerals  being  substantially  identical  in 
chemical  composition,  though  differing  in  crystalline  form. 

7.  In  many  cases,  a  change  of  constitution ;  for  the 
ingredients  subjected  to  the  metamorphic  process  often 
enter  into  new  combinations ;  as  when  a  limestone,  with 
its  impurities  of  clay,  sand,  phosphates,  and  fluorides, 
gives  rise,  under  the  action  of  heat,  not  merely  to  white 
granular  limestone,  but  to  various  crystalline  minerals 
disseminated  through  it,  such  as  mica,  feldspar,  scapolite, 
pyroxene,  apatite,  chondrodite,  etc. 

It  is  thus  seen  that  metamorphism  may  fill  a  rock  with 
crystals  of  various  minerals.  Even  gems  are  often  among 
its  results.  What  is  of  more  value,  it  makes  out  of  rude 
sandstones  and  limestones  crystalline  rocks,  as  granite  and 
marble,  for  architectural  and  other  uses.  Man's  imita- 
tions of  nature  are  seen  in  his  little  red  bricks. 

Process.  —  The  principal  agencies  in  metamorphism  are 
heat,  water,  and  mechanical  action. 

Heat  is  important :  (1)  in  order  to  produce  that  weak- 
ening of  cohesion  among  the  particles  of  a  rock  which  is 
the  preparatory  step  toward  a  recrystallization  ;  and  (2) 
in  order  to  bring  about  the  chemical  changes  that  are 
required,  nearly  all  demanding  a  higher  than  the  ordinary 
temperature,  though  less  than  that  of  complete  fusion. 

Water  is  important  because :  (1)  dry  rocks  (as  illus- 
trated in  a  fire-brick)  are  bad  conductors  of  heat ;  (2)  it 
helps  greatly  in  the  weakening  of  cohesion ;  (3)  it  takes 
up  silica  and  alkali  from  all  rocks  containing  feldspar 
(page  187),  if  heated  (and  little  heat  is  necessary),  and 
thus  becomes  a  siliceous  solution,  which,  on  cooling,  may 
deposit  the  silica  as  a  cement  among  the  grains  of  the 
rock,  and  so  promote  its  solidification  —  as  in  altering 
sandstone  to  quartzite,  —  and  may  also  deposit  quartz  in 
cavities  or  fissures  ;  (4)  at  higher  temperatures,  in  the 


194  DYNAMICAL  GEOLOGY. 

state  of  steam  of  high  pressure,  it  decomposes  readily 
many  of  the  silicates,  or  the  ordinary  minerals  of  rocks, 
and  so  prepares  for  the  formation  of  new  minerals  —  thus 
making  sometimes  feldspar,  mica,  hornblende,  etc.  The 
quartz  grains  of  a  sandstone  have  often  been  converted 
into  minute  crystals  of  quartz  by  the  deposition  of  silica 
over  the  exterior. 

The  water  is  for  the  most  part  that  contained  in  the  rocks 
themselves  ;  for  beds  of  sandstone,  limestone,  etc.,  con- 
tain, before  alteration,  on  an  average  at  least  2  per  cent  of 
water  (independently  of  any  in  spaces  between  the  beds), 
which  means  2  pints  of  water  to  100  pounds  of  the  rock. 

The  heat  is  (1)  partly  the  result  of  mechanical  action  ; 
for  metamorphism  has  generally  taken  place  where  the 
rocks  have  undergone  shoving,  folding,  and  faulting,  and 
sometimes  crushing  (see  page  218) :  and  (2)  partly  also,  the 
heat  of  the  earth's  interior  conducted  upward  into  the  beds 
(page  217) ;  for  metamorphism  has  generally  taken  place 
where  the  strata  have  accumulated  to  very  great  depth. 

These  are  some  of  the  various  ways  in  which  heat  and 
water  have  operated  in  metamorphic  changes.  Direct 
experiments  have  shown  that  crystallization  does  result 
from  the  action  of  heat  and  water.  Quartz  crystals,  feld- 
spar, mica,  and  other  minerals  have  been  artificially  made 
by  the  subjection  of  the  ingredients  to  highly  heated 
moisture. 

Alkaline  waters  dissolve  silica  even  at  very  moderate 
temperatures  ;  and,  wherever  such  solutions  exist,  they 
may  work  at  consolidating,  altering,  and  dissolving  min- 
erals, and  making  geodes  and  veins  of  quartz.  Large 
corals  in  Florida  have  been  hollowed  out  by  this  means, 
and  the  cavities  lined  with  quartz  crystals  or  agate. 
The  fossils  of  a  limestone  have  been  silicified  and  flint 
nodules  made  even  in  cold  waters.  The  ordinary  decom- 
position of  a  feldspar  or  mica,  of  hornblende  or  pyroxene 
—  one  or  more  of  which  silicates  occur  as  constituents  of 
granite,  syenite,  trap,  porphyry,  trachyte,  and  tufa,  — sets 


HEAT.  195 

free  silica  to  make  opal  or  quartz ;  and,  in  some  tufas  of 
California  and  Colorado,  the  clustered  tree  trunks  of  'a 
former  forest,  as  well  as  scattered  logs  and  stumps,  have 
been  petrified  by  silica  from  such,  a  source. 

Pressure  is  requisite  for  most  metamorphic  changes. 
Limestone  heated  without  pressure  loses  its  carbonic  acid 
and  becomes  quicklime  ;  but,  under  pressure,  as  has  been 
proved  by  experiment,  the  carbonic  acid  is  not  driven  off. 
The  needed  pressure  may  be  that  of  an  ocean  above  ;  it 
may  be  that  of  the  superincumbent  rocks,  and  a  few  hun- 
dred feet  would  suffice. 

Crustal  movements  have  operated  in  metamorphism, 
partly  by  producing  heat  through  the  crushing  of  rocks, 
but  also  by  producing  rearrangement  of  the  materials  of 
rocks.  The  schistose  structure,  which  is  so  characteristic 
of  metamorphic  rocks,  is  doubtless  often  produced  in  this 
way  (dynamic  metamorphism).  Sometimes  the  crystalline 
plates  of  mica  and  other  minerals  are  forced  by  pressure 
into  a  position  at  right  angles  to  the  direction  of  pressure  ; 
sometimes  the  rock  has  been  sheared,  and  the  crystalline 
plates  drawn  out  along  the  planes  of  shearing. 

The  similarity  of  an  argillaceous  sandstone  to  gneiss  or 
granite  is  often  much  greater  than  appears  to  the  eye. 
When  a  sandstone  has  been  made  out  of  a  gneiss,  it  may 
have  the  quartz,  feldspar,  and  mica  of  the  gneiss,  merely 
pulverized,  with  little  or  no  chemical  alteration  ;  so  that 
the  change  produced  in  it  by  metamorphism  may  be  mainly 
a  change  in  state  of  crystallization.  By  simply  heating  a 
bar  of  steel,  arid  cooling  it  slowly  or  rapidly,  it  may  be 
made  coarse  or  fine  steel,  the  process  causing  the  molecules 
of  the  small  grains  to  unite  into  larger  grains  in  the  coarser 
kind,  and  the  reverse  for  the  finer.  There  is  something 
analogous  in  the  change,  above  described,  of  an  argilla- 
ceous sandstone  to  gneiss  or  granite.  It  cannot  be  as- 
serted, however,  that  the  feldspar  grains  in  the  sandstone 
will  always  remain  feldspar  ;  they  may  contribute  to  the 
making  of  mica  or  some  other  mineral. 


196  DYNAMICAL  GEOLOGY. 

Often,  however,  the  material  derived  from  the  wear  of 
gneiss  and  granite  and  other  rocks  is  not  only  pulverized, 
but  also  more  or  less  decomposed.  The  feldspar,  for  exam- 
ple, may  have  lost  its  alkalies,  or  the  mica  its  oxide  of 
iron  and  alkalies  ;  and  in  such  a  case  the  process  of  meta- 
morphism  cannot,  of  course,  restore  the  original  rock. 
The  new  rock  made  can  contain  no  feldspar  or  mica,  if 
the  alkalies  have  been  wholly  removed,  but  it  may  turn 
out  an  argillite  or  slate  ;  or,  if  much  oxide  of  iron  and 
magnesia  are  present,  a  hornblende  rock,  or  a  chlorite 
rock,  or  some  other  kind  from  which  the  alkalies,  potash 
and  soda,  are  absent. 

4.  FORMATION  OP  VEINS. 

Nature  and  Origin  of  Spaces  occupied  by  Veins.  — > 
Veins,  like  dikes,  are  fillings  of  spaces  in  the  rocks  ;  but 
they  differ  from  dikes  in  the  manner  in  which  the  filling 
has  taken  place.  Dikes,  as  explained  on  page  188,  are  fis- 
sures filled  with  igneous  rock  injected  in  a  state  of  fusion. 
The  mode  of  formation  of  veins  will  be  explained  later. 

The  spaces  filled  by  veins  are  usually  cracks  or  fissures 
made  (1)  by  uplifting  or  disturbing  forces  ;  (2)  by  the 
expansion  or  pressure  of  vapors  ;  (3)  by  shrinkage  from 
cooling  or  drying  ;  they  may  be  (4)  openings  between 
the  layers  or  laminse  of  a  rock  produced  in  the  flexing  of 
the  beds,  like  those  between  the  leaves  of  a  quire  of  paper 
when  folded  over ;  or  (5)  open  spaces  made  in  rocks  by 
solution,  as  caverns  are  made. 

The  uplifting  and  flexing  of  rocks  which  have  resulted 
in  fissures  and  openings,  are  often  accompaniments  of 
metamorphic  change,  and  the  fissures  may  have  become 
filled  before  the  era  of  metamorphism  had  passed.  The 
heat  concerned  in  such  a  case  may  be,  as  explained  above, 
that  derived  from  the  movements  in  the  strata,  in  connec- 
tion with  that  of  the  earth's  depths. 

Veins  are  large  or  small,  deep  or  shallow,  single  or  like 
a  complex  network,  according  to  the  character  of  the 


HEAT. 


197 


fractures  in  which  they  were  formed.  They  may  be  as 
thin  as  paper,  or  they  may  be  rods  in  thickness.  Figs. 
200-203  represent  some  of  the  forms.  In  Fig.  200, 


FIGS.  200-205. 


201 


202 


203 


204 

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205 


Veins. 


there  are  two  veins,  a  and  £;  in  Fig.  201,  a  network  of 
thin  veins ;  in  Fig.  202,  two  veins,  a,  a',  of  very  irregular 
form — a  kind  not  uncommon,  —  and  another,  5,  intersect- 
ing one  of  these  ;  in  Fig.  203,  two  large  veins,  of  still 
more  irregular  character,  crossing  one  another. 


198  DYNAMICAL  GEOLOGY. 

Materials  of  Veins.  —  Quartz  is  the  most  common,  be- 
cause siliceous  solutions  are  easily  made,  requiring  little 
heat.  Granitic  material,  requiring  higher  heat,  is  also 
common,  but  especially  in  veins  intersecting  the  more 
crystalline  rocks;  and  vein  granite  is  usually  much  coarser 
in  crystallization  than  ordinary  granite.  Other  materials 
of  frequent  occurrence  are  calcite,  barite  (barium  sul- 
phate) and  fluorite  (calcium  fluoride);  but,  where  these 
occur,  quartz  may  also  be  present.  Along  with  the  earthy 
minerals  may  occur  gold,  or  various  ores  of  copper,  lead, 
silver,  and  other  metals,  besides  pyrite  (iron  sulphide), 
which  is  almost  universally  present  in  ore-bearing  veins, 
or  lodes.  The  earthy  minerals  are  called  the  gangue  of 
the  ore. 

Many  veins  have  a  banded  structure,  like  Figs.  204  and 
205.  Metallic  veins,  especially,  are  often  thus  banded, 
and  have  the  ores  lying  in  one  or  more  bands  alternating 
with  other  bands  consisting  of  different  minerals  or  rock 
material. 

In  Fig.  204,  representing  a  vein  at  Valparaiso,  the 
bands  numbered  1,  3,  and  6  are  quartz  ;  the  others  are 
granite.  In  Fig.  205,  representing  a  vein  at  Godolphin 
Bridge,  Cornwall,  a  is  a  band  of  quartz,  £,  b  are  bands  of 
agate,  c  is  crystallized  quartz,  d  is  chalcopyrite  mixed  with 
quartz. 

Origin  of  Vein  Deposits.  —  The  material  of  veins  has 
been  deposited  from  solutions  or  vapors.  The  solutions 
or  vapors  are  generally  hot.  This  is  always  the  case  in 
large  veins,  or  in  veins  extending  down  to  any  consider- 
able depth.  Such  veins  may  be  divided  into  two  classes, 
according  to  the  source  of  the  heat. 

1.  Where  the  Heat  is  not  Derived  from  Eruptions  of 
Igneous  Hock.  —  Such  veins  are  apt  to  occur  in  regions 
of  metamorphic  rock ;  and  the  heat,  like  that  in  regional 
metamorphism,  is  the  result  of  movements  in  the  earth's 
crust,  or  is  the  general  heat  of  the  interior  of  the  globe. 
In  this  class  are  included  nearly  all  veins  of  quartz  and 


HEAT.  199 

granite,  whether  containing  metallic  ores  or  not,  and 
most  banded  mineral  veins.  The  fissures  or  openings  are 
a  result  of  profound  disturbances,  such  as  give  rise  also  to 
metamorphism.  The  material  of  the  vein  is  brought  into 
the  opening  either  from  the  rocks  directly  adjoining,  or 
from  those  of  depths  below.  The  fissured  rocks  being 
heated,  as  above  stated,  all  water  or  vapor  present  tends 
to  decompose  the  rock  material  near  the  fissure  ;  it  takes 
alkalies  from  the  feldspars,  and  so  becomes  siliceous,  and 
few  minerals  will  withstand  its  action.  The  water  or 
vapor  presses  into  the  fissures  or  openings,  carrying  the 
mineral  material  it  can  dissolve,  and  depositing  it ;  and  it 
keeps  on  supplying  material  until  the  fissure  is  filled  or 
the  supply  of  material  is  exhausted.  It  is  natural  that 
veins  in  gneiss  and  mica  schist  filled  in  this  way  should 
often  be  granitic  veins,  for  these  rocks  contain  the  quartz, 
feldspar,  and  mica  of  granite  ;  and  that  they  should  often 
be  quartz  veins  simply,  which  they  are  likely  to  be  if  the 
temperature  is  not  high  enough  to  make  or  dissolve  feld- 
spar and  mica.  The  veins  of  extremely  coarse  granite,  or 
pegmatite,  appear  to  be  in  origin  somewhat  intermediate 
between  ordinary  veins  and  dikes.  Under  the  joint  action 
of  heat  and  water,  the  material  was  probably  in  a  condi- 
tion somewhat  intermediate  between  fusion  and  solution. 
The  various  phases  of  aqtieo-igneous  fusion  form,  in  fact,  a 
complete  series  of  gradations  between  fusion  and  solution. 

Under  the  action,  whatever  metallic  ores  or  constituents 
of  gems  the  fissured  rock  contains,  are  carried  into  the 
fissure  with  the  other  mineral  material;  and  additions  may 
be  received  largely  through  solutions  or  vapors  rising 
from  its  deeper  parts. 

By  such  means  veins  have  been  supplied  with  their  gems 
and  ores.  The  quartz  veins  in  the  slate  rocks  of  a  gold 
region  have  in  this  way  become  gold-bearing  veins,  the 
gold  and  quartz  having  been  brought  in  by  the  same 
moisture,  and  both  having  been  gathered  from  the  adjoin- 
ing or  underlying  rocks.  These  openings,  in  the  case  of 


200  DYNAMICAL   GEOLOGY. 

auriferous  quartz  veins,  were  often  openings  between  layers 
of  the  slate  made  in  the  folding  or  upturning.  Quartz 
veins  are  the  usual  original  sources  of  gold;  and  the  gold- 
bearing  gravels,  which  afford  the  metal  by  simple  washing, 
and  have  yielded  the  larger  part  of  the  gold  in  use,  are 
the  detritus  made  out  of  the  gold-bearing  rocks.  The 
same  gravels  often  afford  platinum,  iridium,  and  diamonds. 

While  fissures  filled  by  this  lateral  inflow  of  material,  in 
connection  with  emanations  from  the  depths  below,  may 
be  uniform  in  material  across,  as  in  many  quartz  veins, 
they  may  also  consist  of  bands  of  different  minerals,  as  in 
many  metallic  veins  (Figs.  204,  205).  In  the  formation 
of  banded  veins,  the  process  has  brought  in  for  a  while 
one  kind  of  mineral,  as  quartz,  and  deposited  it  over  the 
walls  of  the  fissure ;  then,  through  some  change,  some 
other  mineral  or  ore,  as  an  ore  of  lead,  or  one  of  zinc,  or 
one  of  copper ;  then  quartz  again,  or  fluorite,  or  calcite  ; 
and  so  on  until  the  fissure  was  filled.  In  a  normal  banded 
vein  the  succession  of  bands  from  each  side  to  the  middle 
is  identical  or  nearly  so,  as  illustrated  in  Fig.  204.  In  the 
case  shown  in  Fig.  205,  the  fissure  appears  to  have  been 
opened  and  filled  at  two  different  times,  the  band  d  being 
virtually  a  separate  vein  from  the  adjoining  bands  6,  e,  b. 

The  above  is  one  of  the  methods  by  which  the  earth's 
precious  metals  have  been  gathered  out  of  the  rocks,  in 
which  they  were  sparingly  disseminated,  into  generous 
veins,  and  thereby  placed  within  reach  of  the  miner. 

2.  Where  the  Heat  is  Derived  from  Eruptions  of  Igneous 
Rock.  —  (a)  Dikes  of  porphyry,  dolerite,  and  related  rocks 
sometimes  determine  the  courses  of  veins  of  metallic  ores. 
The  veins  are  generally  situated  near  the  walls  of  the -dike, 
and  either  in  the  igneous  rock  or  in  the  rock  adjoining. 

The  veins  (1)  may  have  been  made  when  the  dike  was 
made ;  or  (2)  they  may  occupy  fissures  made  subsequently, 
but  during  the  same  epoch  of  disturbance  ;  or  (3)  they 
may  have  been  formed  later,  the  old  plane  of  fracture 
being  a  plane  of  weakness  liable  to  be  opened  anew.  The 


HEAT.  201 

metallic  materials  of  the  vein  have  been  brought  up  as 
solutions  or  vapors,  either  from  the  depths  that  afforded 
the  igneous  rock  itself,  or,  more  probably,  from  the  walls 
of  a  deep  part  of  the  fissure. 

The  veins  of  native  copper  at  Keweenaw  Point,  those 
containing  ores  of  the  same  metal  in  the  red  sandstone 
(Triassic)  of  the  Connecticut  Valley,  New  Jersey,  and 
Pennsylvania,  those  of  silver  ores  in  Nevada  and  other 
localities  along  the  Rocky  Mountains  and  Andes,  thus 
originated  —  that  is,  in  connection  with  igneous  ejections; 
the  ores  not  coming  up  as  a  constituent  part  of  the 
igneous  rock,  but  through  the  agency  of  vapors  and  sub- 
terranean waters. 

(6)  Frequently,  in  regions  of  igneous  ejections,  fissures 
have  been  made  that  have  received  not  igneous  rock,  but 
only  vapors  or  mineral  solutions  from  below,  and  thus 
have  become  metallic  veins.  Each  of  the  regions  just 
mentioned  contains  examples  of  such  veins. 

The  filling  may  continue  in  progress  long  after  the 
igneous  rock  is  cooled,  or  as  long  as  hot  water  or  vapor 
continues  to  rise  through  the  fissure.  Shrinkage  cracks 
and  other  openings  in  the  rock  adjoining  the  fissure 
may  spread  the  mineral  depositions  widely  on  either  side. 
The  vent  may  continue  as  a  source  of  heat  to  surface 
waters,  making  hot  mineral  springs  and  steaming  pools 
or  basins,  about  or  from  which  deposits  may  take  place 
of  a  veinlike  character,  as  is  going  on  now  in  Nevada  and 
California. 

Superficial  Veins.  —  Besides  the  veins  thus  far  con- 
sidered, which  occupy  fissures  extending  to  some  consid- 
erable depth,  and  whose  formation  involves  the  action  of 
heat  in  considerable  degree,  there  are  numerous  small 
superficial  veins  which  may  have  been  formed  without 
any  considerable  elevation  of  temperature.  •  Shrinkage 
cracks  and  other  small  cracks  in  rocks  have  been  filled 
with  calcite  or  other  minerals  brought  in  by  infiltrating 
waters  from  the  immediate  vicinity. 


202  DYNAMICAL  GEOLOGY. 

Depositions  of  galenite,  or  lead  ore  (sometimes  with 
zinc  ores),  have  taken  place  in  cavities  or  caverns  in  lime- 
stones, as  in  Wisconsin,  Illinois,  and  Missouri.  In  these 
deposits,  the  source  of  the  ore  is  somewhat  uncertain;  but  it 
is  apparently  derived  from  the  concentration  of  ores  which 
had  been  diffused  through  the  sedimentary  strata,  since 
the  cavities  do  not  have  the  character  of  fissures  extending 
to  great  depths.  Such  deposits  often  have  great  extent, 
and  are  a  valuable  source  of  ore,  as  in  the  localities  men- 
tioned. During  the  deposition  of  the  ores,  the  limestone 
underwent  much  corrosion  from  acid  solutions  concerned 
in  or  resulting  from  the  process. 

Many  cases  of  extensive  bodies  of  ore  in  cavities  in 
limestone  appear  not  to  be  of  the  above-mentioned  kind, 
but  to  be  vein  deposits  of  the  ordinary  sort.  They  may 
in  some  cases  have  originated  in  fissures  which  produced 
ore  deposits  only  where  they  intersected  limestones,  be- 
cause only  limestones  were  easily  rendered  cavernous  by 
the  corroding  waters  or  vapors,  so  as  to  afford  spaces  for 
the  ores. 

So-called  Veins  that  are  not  True  Veins.  —  In  the 
course  of  the  earth's  rock-making,  metallic  ores  have 
often  been  deposited  along  with  the  detritus  when  a 
sedimentary  bed  was  in  progress  of  formation ;  they 
have  been  brought  into  marshes,  or  spread  over  confined 
sea  margins  and  mud  flats,  by  running  waters  which  took 
up  the  metal  (in  some  soluble  state  of  combination)  from 
the  decomposing  rocks  of  the  region  around.  Deposits  of 
iron  ores  are  thus  made  at  the  present  time  (page  116),  and 
ores  of  zinc,  cobalt,  nickel,  and  copper  were  so  deposited 
in  early  geological  ages.  When  strata  containing  such 
metalliferous  layers  have  undergone  uplifts  and  crystalli- 
zation, the  nearly  vertical  beds  look  like  veins.  Many 
of  the  great  deposits  of  hematite  and  magnetite  in  the 
Archaean  terranes  are  probably  beds,  not  veins  nor  dikes. 

Wide  cracks  opening  to  the  surface  have  sometimes  been 
filled  with  sand  or  earth.  Such  deposits  have  sometimes 


CEUSTAL  MOVEMENTS.  203 

been  called  false  veins.  They  have  the  character  of  neither 
veins  nor  dikes,  though  both  these  names  have  been  applied 
to  them. 

VI.    CRUSTAL    MOVEMENTS;    EVOLUTION   OF 
CONTINENTS   AND   MOUNTAINS. 

Explanations  already  given.  —  In  the  preceding  chapters 
the  origin  of  many  geological  phenomena,  and  of  some 
of  the  earth's  features,  have  been  briefly  explained. 

1.  Changes  of  level  have  been  described  as  caused  (1)  by 
change  of  temperature,  this  cause  producing  the  expan- 
sion and  contraction  of  rocks  (page  172) ;   (2)  by  under- 
mining due  to  subterranean  water   (page  144);    (3)  by 
undermining  due  to  volcanic  outflows  (page  184). 

2.  Mountain  forms  have  been  described  as  often  a  result 
)f  the  sculpturing  of  elevated  plateaus  of  nearly  horizontal 

>ck  by  streams,  as  exemplified  among  some  of  the  most 
lajestic  mountains  of  the  globe  (page  133). 

3.  Folding  of  beds  has  been  shown  to  have  been  caused, 
rhen  they  are  clayey,  soft,  and  wet,  by  a  lateral  move- 
lent  produced  through  the  pressure  of  superincumbent 
taterial  (page  146). 

4.  Fractures  and  faultings    of   strata    have    been    at- 
tributed (1)  to  undermining  by  different  methods  (pages 
144,  184);   (2)  to  contraction  or  expansion  by  change  of 
temperature  ;  (3)  to  shrinkage  on  drying,  producing  deep 
or  shallow  fractures  (page  174);    (4)  to  the  expansive 
force  of  vapors  (page  182);   (5)  to  the  hydrostatic  pres- 
sure  of   a   column   of   lava   (page   180)  ;    and  to   other 
causes. 

5.  MetamorpMsm  has  been  described  as  produced  on  a 
small  scale,  (1)  in  the  vicinity  of  dikes  of  igneous  rock, 
through  the  heat  of  the  rock  when  it  was  cooling  from 
fusion,  if  vapors  or  moisture  were  present  to  aid  (page  190) ; 
and  (2)  in  the  neighborhood  of  hot  springs  (page  191). 
Metamorphism  on  a  large  scale  (regional  rnetamorphism) 


204  DYNAMICAL   GEOLOGY. 

has  been  said  to  occur  in  connection  with  great  crustal 
movements  (p.  195);  but  no  explanation  has  been  given  of 
the  cause  of  those  movements. 

6.  Earthquakes  have  been  stated  to  result  from  frac- 
tures of  rocks  in  subterranean  regions,  consequent  (1)  on 
undermining  by  the  solvent  action  of  water  (page  144), 
or  by  the  extrusion  of  lava  (page  184);  or  (2)  on  the 
explosions  attending  volcanic  action  (page  182). 

But  none  of  the  causes  that  have  been  considered  explain 
the  great  changes  of  level  involving  large  parts  of  conti- 
nents or  of  oceanic  areas  ;  or  the  phenomena  attending  the 
making  and  uplifting  of  mountain  ranges ;  or  the  earth- 
quakes that  have  shaken  a  hemisphere. 

Relation  in  Size  between  the  Earth  and  its  Surface 
Features.  —  On  a  globe  twelve  feet  in  diameter,  the  height 
of  the  earth's  loftiest  mountains  would  be  represented  by 
an  elevation  of  about  one  tenth  of  an  inch ;  the  whole 
difference  of  level  between  the  deepest  part  of  the  oceanic 
basin  and  the  highest  point  of  the  land,  by  twice  this 
amount ;  and  the  mean  depth  of  the  ocean,  by  a  depression 
of  one  nineteenth  of  an  inch.  The  deformation  of  the 
sphere  produced  in  the  making  of  the  continents  and 
mountains  was,  therefore,  very  small. 

Probable  Condition  of  the  Earth's  Interior.  —  It  is  almost 
certain  that  the  central  portions  of  the  earth  are  now 
solid.  The  enormous  pressure  in  those  central  portions 
would  raise  the  melting  point  far  above  any  tempera- 
ture which  can  be  supposed  to  exist  there.  Indeed,  it  is 
probable  that  when  the  material  of  the  globe  first  aggre- 
gated itself  together,  the  central  portions  were  already 
solid  from  the  effect  of  pressure,  so  that  the  earth  has 
never  been  completely  liquid.  Whether  there  is  now,  as 
presumably  there  once  was,  a  liquid  stratum  between  the 
solid  nucleus  and  the  solid  crust,  is  a  question  on  which 
there  is  much  difference  of  opinion. 

It  is  urged  by  many  physicists,  though  not  by  all,  that 
the  earth  has  become  solid  throughout,  as  solid  as  steel; 


CRUSTAL  MOVEMENTS.  205 

the  conclusion  being  based  on  the  ground  that,  if  the 
earth  were  liquid  within,  the  crust  would  yield  in  con- 
siderable degree  to  the  tide-producing  force  of  the  moon 
and  sun,  and  hence  the  tides  of  the  ocean  would  be  dif- 
ferent in  amount  from  what  they  actually  are. 

It  is  claimed,  on  the  other  hand,  that  geological  facts 
cannot  be  explained  on  the  basis  of  absolute  solidity. 
Great  subsidences,  like  that  of  30,000  feet  or  more,  which 
was  a  prelude  to  the  making  of  the  Appalachians,  cer- 
tainly suggest  the  idea  that  plastic  rock  exists  beneath,  to 
be  pushed  aside  so  as  to  render  subsidence  possible. 
Many  have  urged  that  there  must  have  been  in  past  time 
a  plastic  layer  between  the  crust  and  a  solid  nucleus,  or  at 
least  the  remains  of  such  a  plastic  layer,  wherever  the 
great  movements  have  taken  place.  This  argument,  how- 
ever, is  weakened  by  the  consideration  that  solid  metal 
and  rock,  when  under  pressure,  yield  through  molecular 
movement,  as  first  illustrated  by  Tresca.  When  holes  are 
punched  in  plates  of  cold  iron,  the  cores  punched  out  may 
be  less  than  half  the  thickness  of  the  plates,  and  not  in- 
creased in  density,  showing  that  there  has  been  a  flow  of 
the  metal  outward  from  the  punch.  In  this  way  the 
apparent  plasticity  of  the  subcrustal  regions  may  proba- 
bly be  explained. 

Moreover,  it  is  claimed  that,  if  a  plastic  layer  exists,  and 
the  crust  above  it  is  thin  —  say  twenty-five  miles,  —  the 
crust  would  rest  on  the  mobile  sea  underneath  it  like  a 
floating  mass,  and  hence  it  would  be  pressed  down  by  any 
local  addition  to  its  weight,  however  slight ;  that  it  could 
not  sustain  mountain  elevations,  unless  the  loAver  part  of 
the  crust  beneath  the  mountain  were  flexed  downward 
as  the  upper  part  was  flexed  upward.  It  seems  to  be 
evident  that,  with  a  crust  so  mobile  as  above  described, 
the  lateral  pressure  generated  within  it  could  have  pro- 
duced no  long  range  of  mountains  under  one  common 
method  of  action ;  nothing  of  that  uniformity  of  results 
exhibited  in  many  great  regions  from  Archaean  time 


206  DYNAMICAL  GEOLOGY. 

onward ;  no  mountain  borders  for  the  continents ;  no 
general  system  of  feature  lines  for  the  globe. 

The  facts  would  appear,  therefore,  to  prove  that,  if  a 
liquid  or  plastic  subcrustal  layer  exists,  the  crust  must 
be  thick  enough  to  possess  some  considerable  degree  of 
rigidity.  And,  probably,  whatever  the  condition  of  the 
plastic  layer  underneath  the  crust  may  have  been  in  past 
time,  only  mere  remnants  of  it  now  exist,  the  greater 
part  of  it  (if  not  the  whole)  having  become  solid. 

On  the  supposition  that  the  liquid  subcrustal  layer 
which  once  existed  has  mostly  solidified,  there  must  still 
remain,  at  no  great  depth,  a  zone  where  the  temperature  is 
just  below  the  melting  point,  and  where  fusion  would  be 
produced  by  any  local  diminution  of  pressure  or  increment 
of  heat,  such  as  might  result  from  movements  of  the  crust. 
Such  regions  of  liquefaction  may  furnish  the  supplies  for 
volcanoes  and  other  forms  of  igneous  eruption. 

Evolution  of  the  Earth's  Fundamental  Features. 

Whether  its  interior  be  substantially  solid,  or  exten- 
sively liquid,  the  earth  is  believed  to  be  capable  of  adjust- 
ment to  gravitational  pressure  through  molecular  flow, 
and  to  owe  its  shape  primarily  to  the  principle  of  gravita- 
tional equilibrium.  The  condition  of  equilibrium  to  which 
gravitation  tends  to  reduce  the  earth  has  been  called  by 
Button  isostasy. 

Origin  of  Continent  and  Ocean.  —  The  greatest  ine- 
qualities of  the  earth's  surface  —  continental  plateaus  and 
oceanic  basins  —  are  probably  dependent  on  the  principle 
of  isostasy.  Observations  on  the  force  of  gravity  in  dif- 
ferent localities  appear  to  show  that  the  materials  under- 
lying the  oceans  are  denser  than  those  underlying  the 
continents.  The  downward  pressure  on  the  oceanic  radii 
may  thus  equal  that  on  the  continental  radii,  the  denser 
material  compensating  for  the  inferior  height  of  the 
column. 

On  this  view,  the  distinction  between  the  continental 


CBUSTAL  MOVEMENTS.  207 

plateaus  and  the  oceanic  basins  must  have  been  deter- 
mined by  the  original  distribution  of  material  in  the  mass 
of  the  earth.  Hence  continents  and  oceans  must  have 
been  substantially  permanent.  Though  the  continental 
plateaus  have  been  extensively  covered  by  shallow  seas, 
they  have  probably  always  been  for  the  most  part  ele- 
vated regions  as  compared  with  the  real  oceans. 

Origin  of  Mountain  Ranges.  —  It  is  here  assumed  that 
the  cause  of  the  movements  in  mountain-making  is  the 
contraction  of  the  cooling  globe.  Although  that  theory 
is  not  without  difficulties,  and  is  not  universally  accepted, 
it  gives  a  far  more  satisfactory  explanation  of  the  facts 
than  any  other  theory  which  has  been  proposed. 

That  contraction  must  be  going  on  within  the  earth, 
follows  from  the  high  temperature  which  has  been  shown 
to  exist  there.  Heat  must  escape  to  the  surface  by  con- 
duction, and  there  appears  to  be  no  internal  source  of 
heat  which  can  make  good  the  loss.  Hence  the  earth's 
skin,  like  that  of  a  drying  and  shriveling  apple,  comes  to 
be  continually  too  large  for  the  shrinking  interior. 

Location  of  Mountain  Chains.  —  The  compressive  force 
is  universal  in  the  superficial  zone  of  the  earth.  Never- 
theless, the  wrinkles  which  result  from  it  have  in  general 
a  direct  reference  to  continental  lines. 

The  oceanic  area,  besides  being  much  depressed  below 
the  continental,  has  rather  abrupt  sides,  as  explained  on 
page  12.  The  change  of  curvature  of  the  surface  along 
the  borders  between  continents  and  oceans  must  have 
made  those  borders  lines  of  weakness  in  the  crust.  The 
lateral  pressure  in  the  crust  being  universal  over  the 
sphere,  but  greatest  in  the  oceanic  basins,  since  these  have 
always  been  the  regions  of  greatest  subsidence,  the  force 
in  the  oceanic  crust  must  have  acted  obliquely  upward 
against  the  crust  of  the  continental  border.  The  action 
was  that  of  a  shove  or  thrust  from  the  direction  of  the 
ocean,  and  in  each  oceanic  area  was  somewhat  proportional 
to  its  extent ;  consequently,  bendings,  uplifts,  fractures, 


208  DYNAMICAL   GEOLOGY. 

foldings  of  strata,  earthquakes,  mountain-making,  became 
eminently  features  of  the  continental  borders,  and  most 
prominently  so  of  the  borders  which  face  the  largest 
oceans. 

Continental  Evolution,  as  illustrated  in  North  Amer- 
ica. —  The  two  systems  of  forces  engaged  in  the  progress 
of  North  America  were  those  from  the  direction  of  the 
Atlantic  and  the  Pacific  basin  —  the  latter  the  greater. 
Under  their  action  the  V-shaped  Archaean  area  (see  map, 
page  237)  was  first  defined,  one  branch  stretching  north- 
eastward to  Labrador  and  the  other  northwestward  to  the 
Arctic  seas,  and  thus  facing  respectively  the  Atlantic  and 
Pacific  areas,  while  linear  areas  of  Archaean  rock  extend, 
in  a  series  approximately  parallel  with  the  eastern  arm  of 
the  V,  from  Newfoundland  to  Georgia,  and,  in  another 
series  approximately  parallel  with  the  western  arm  of  the 
V,  along  the  course  of  the  western  Cordillera.  It  follows 
from  the  courses  of  the  arms  of  the  V,  and  of  the  other 
Archaean  areas,  that  the  Atlantic  force  acted  mainly  from 
the  southeastward,  and  the  Pacific  from  the  southwest- 
ward,  and  the  two,  therefore,  nearly  at  right  angles  to 
one  another.  It  is  also  apparent  that  the  Pacific  force 
even  then  was  the  greater,  and  hence  the  Pacific  Ocean 
the  larger ;  for  the  northwestward  brancn  of  the  V  is  far 
the  longer. 

Thus  the  Archaean  nucleus  was  outlined,  and  the  posi- 
tion of  Hudson  Bay  determined  within  the  arms  of  the  V. 
From  this  nucleal  dry  land  progress  went  forward  south- 
eastward, or  toward  the  Atlantic,  and  southwestward, 
or  toward  the  Pacific,  successive  formations  being  added, 
and  the  dry  land  gradually  extending  (though  with  many 
oscillations)  under  changes  of  level  caused  mainly  by  the 
same  forces. 

Then,  when  the  Lower  Silurian  closed,  appeared  the 
mountains  of  the  Taconic  system  ;  and,  when  Paleozoic 
time  was  closing,  appeared  the  Appalachian  system, 
parallel  to  the  eastern  branch  of  the  Archaean  heights. 


CRUSTAL   MOVEMENTS.  209 

Again,  on  the  Pacific  side,  other  ranges  were  made, 
parallel  to  the  course  of  the  Rocky  Mountain  chain ; 
among  them  —  after  the  Jurassic  era,  the  Sierra  Nevada ; 
after  the  Cretaceous  era,  the  ranges  of  the  Laramide 
system ;  and,  still  later,  Tertiary  ranges  toward  the  coast, 
each  epoch  adding  new  parallels  to  the  western  branch  of 
the  Archaean  nucleus.  Finally,  in  the  course  of  the  Ter- 
tiary era,  occurred  the  vast  geanticlinal  movement  in 
which  the  mass  of  the  Rocky  Mountains  rose  to  its  full 
height  above  the  ocean. 

Each  added  range,  as  is  seen,  proves  that  the  mountain- 
making  forces  continued  to  act  to  a  large  degree  from  the 
same  directions  as  in  Archaean  time. 

Thus  the  continent  made  progress,  adding  layer  after 
layer  to  the  rocks  over  its  surface,  and  range  after  range 
in  parallel  lines  to  its  heights,  until  finally  the  continental 
area  reached  its  limit,  and  the  great  interior  basin  had  its 
mountain  borders  completed  :  on  the  side  of  the  Atlantic, 
the  low  Appalachians ;  on  the  side  of  the  Pacific,  the 
massive  and  lofty  Cordillera. 

On  this  view,  the  evolution  of  the  features  of  the  sur- 
face went  forward  through  one  system  of  forces  originat- 
ing in  one  single  cause  —  the  earth's  contraction  from 
cooling.  North  America,  which  is  here  appealed  to  for 
explanations,  affords  the  truest  and  clearest  illustration  of 
the  principles  involved  in  the  system  of  evolution,  because 
it  lies  alone  between  the  two  oceans.  The  progress  on 
this  account  went  forward  with  great  regularity,  each  age 
repeating  the  preceding  in  the  direction  of  all  oscillations 
or  uplifts.  It  was  a  single  isolated  individual  making 
systematic  progress  throughout  until  its  final  completion, 
and  exhibits  truly  the  system  in  the  earth's  development, 
whatever  the  true  theory  of  that  development.  Europe, 
in  contrast,  has  Africa  on  the  south  and  Asia  on  the  east ; 
it  is,  therefore,  full  of  complexities  in  its  feature  lines,  and 
in  the  succession  of  events  that  make  up  its  geological 
history. 


210  DYNAMICAL  GEOLOGY. 


Structure  of  Mountain  Ranges. 

It  has  already  been  stated  that  mountain-making  move- 
ments result  from  the  compressive  force  exerted  upon  the 
crust  of  the  globe  by  reason  of  the  cooling  and  consequent 
contraction  of  the  hot  material  beneath  ;  and  that  in  gen- 
eral that  force  manifests  itself  most  conspicuously  near 
the  continental  borders  as  a  thrust  from  the  direction 
of  the  oceans.  Before  giving  more  detailed  explanation  of 
the  process  of  mountain-making,  it  is  necessary  to  give 
some  account  of  the  characteristic  structure  of  mountain 
ranges. 

Range,  System,  Chain,  Cordillera.  —  A  mountain  range 
includes  all  the  ridges  resulting  from  a  single  orogenic 
movement  —  that  is,  in  general,  as  will  be  explained  here- 
after (page  216),  the  structure  resulting  from  the  crushing 
and  upfolding  of  a  single  geosyncline.  Ranges  are  the 
individuals  or  units  in  mountain  structure. 

A  mountain  system  includes  all  ranges  in  any  one  region 
made  in  different,  more  or  less  independent,  geosynclines, 
at  the  same  epoch.  Thus  the  Appalachian  range,  the 
Acadian  range  in  Newfoundland  and  Nova  Scotia,  and 
the  Ouachita  range  in  Arkansas  and  the  Indian  Territory, 
form  together  the  Appalachian  system. 

A  mountain  chain  is  a  combination  of  approximately 
parallel  ranges  or  mountain  systems  of  different  epochs. 
Thus  the  Appalachian  chain  is  the  whole  mountain  border 
of  the  Atlantic  side  of  North  America  —  including  high- 
lands of  Archaean  age,  the  Taconic  system  of  mid-Paleo- 
zoic age,  and  the  Appalachian  system  of  post-Paleozoic 
age. 

A  combination  of  two  or  more  mountain  chains  consti.- 
tutes  a  cordillera.  The  complex  mass  which  includes  the 
chain  of  the  Rocky  Mountains  on  the  east,  and  the  Sierra 
Nevada  and  the  Coast  ranges  on  the  west,  is  an  example 
of  a  cordillera. 


CRUSTAL  MOVEMENTS.  211 

The  study  of  the  structure  and  history  of  a  mountain 
range  gives,  then,  an  understanding  of  the  whole  subject, 
since  systems,  chains,  and  Cordilleras  involve  only  repeti- 
tion of  ranges.  The  subject  will  be  illustrated  chiefly 
from  the  Appalachian  range,  extending  (under  various 
names)  from  New  York  to  Alabama — a  typical  and  classi- 
cal example  of  mountain  structure. 

Thickness  of  Strata.  —  A  marked  characteristic  of  moun- 
tain structure  is  the  immense  thickness  of  the  strata. 
The  Paleozoic  strata  of  which  the  Appalachians  are  built 
have  a  thickness  of  30,000  to  40,000  feet,  while  the  strata 
of  the  same  age  in  parts  of  the  Mississippi  Valley  do  not 
exceed  one  tenth  of  that  thickness.  Moreover,  these  strata 
were  all  formed  in  water  of  no  great  depth,  showing  that 
during  their  deposition  occurred  a  progressive  subsidence 
to  a  depth  more  than  twice  the  mean  depth  of  the  ocean. 

Disturbed  Condition  of  the  Strata.  —  The  following 
are  among  the  characteristic  features  of  the  Appalachian 
region :  — 

1.  Strata  have  been  upraised  and  flexed  into  great  folds, 
some  of  the  folds  a  score  or  more  of  miles  in  span. 

2.  Deep  fissures  of  the  earth's  crust  have  been  opened, 
and  faults  innumerable  have  been  produced,  some  of  them 
of  10,000  to  20,000  feet. 

3.  Rocks  have  been  consolidated  ;  and,  in  the  region  of 
the  Green  Mountains,  sandstones  and  shales  have  been 
crystallized   into   gneiss,  mica  schist,  and   other  related 
rocks,   and    limestone    into    architectural    and    statuary 
marble. 

4.  Bituminous  coal  has  been  turned  into  anthracite. 
Figs.  206-210  illustrate  the  folds  and  faults  in  the  strata 

of  the  Appalachian  range. 

•  Figs.  206-208  represent  sections  in  the  coal  regions  of 
Pennsylvania.  In  Fig.  207,  the  Carboniferous  beds  are 
the  uppermost  beds  at  the  left,  numbered  14  ;  the  rest 
are  beds  of  underlying  Paleozoic  formations,  as  explained 
under  the  figure. 


212 


DYNAMICAL   GEOLOGY. 


Fig.  208  represents  a  section  of  the  anthracite  region 
between  Nesquehoning  Valley  (on  the  west,  left  in  section) 


FIG.  206. 


Section  at  Trevorton  Gap,  Pennsylvania,  the  dark  bands  representing  coal  beds. 

and  Mauch  Chunk  (from  the  Report  of  C.  A.  Ashburner, 
of  the  Geological  Survey  of  Pennsylvania  under  Profes- 
sor Lesley).  The  length  is  about  3600  feet  (the  scale 


FIG.  20T. 


Section  on  the  Schuylkill,  Pennsylvania :  P.,  Pottsville ;  2,  Cambrian  ;  3,  4,  Lower  Silurian ; 
5,  Niagara;  7,  Lower  Helderberg;  8,  Oriskany  ;  10,  Hamilton  ;  11,  12,  Upper  Devonian; 
13,  Subcarboniferous ;  14,  Carboniferous. 

of  the  figure  being  1000  feet  to  the  inch).  The  flexures 
to  the  west  have  their  summits  pushed  westward  40°  be- 
yond the  vertical.  The  folded  rocks  consist  of  beds  of 

FIG.  208. 


Section  of  the  Panther  Creek  Anthracite  basin  at  Nesquehoning  tunnel. 

anthracite  and  intervening  strata  of  shale  and  sandstone  ; 
and  the  anthracite  beds  include  the  great  "  Mammoth 
bed"  (lettered  at  its  outcrop  E,  E1,  E2)  which  is  13  to  27 
feet  thick,  and  the  bed  F  (outcropping  also  at  F1.  F2,  F3, 


CRUSTAL   MOVEMENTS. 


213 


F4,  F5),  11  to  20  feet  thick,  besides  one  of  8  to  9  feet. 
The  "  Mammoth  bed  "  is  doubled  on  itself  at  E1. 

Fig.  209  was  taken  from  the  vicinity  of  Bore  Springs,  in 
Virginia,  and  includes  Silurian  and  Devonian  beds. 

Fig.  210  represents  one  of  the  great  faults  in  south- 
ern Virginia  (between  Walkers  Mountain  and  Peak 
Hills)  ;  the  break  is  at  F,  and  the  rocks  on  the  left  were 


vin 


v      vi  v  vi  v  iv     in  11 


S.E. 


H.W.    vi  v    iv         m    ii  m  i 

Section  from  the  Great  North  to  the  Little  North  Mountain  through  Bore  Springs,  Virginia: 
t,  t,  position  of  thermal  springs;  II.-IV.,  Lower  Silurian;  V.,  VI.,  Upper  Silurian; 
VII.,  Devonian. 

shoved  up  along  the  sloping  fracture  until  a  Lower  Silurian 
limestone  (a)  was  on  a  level  with  the  Subcarboniferous 
formation  (c£)  —  a  fault  of  about  8000  feet. 

Such  examples  are  found  in  great  numbers  throughout 
the  Appalachians.  In  many  of  the  transverse  valleys  the 
curves  of  alternating  anticlines  and  synclines  may  bf 
traced  for  scores  of  miles. 


FIG.  210. 


Section  of  the  Paleozoic  formations  of  the  Appalachians  in  southern  Virginia,  betweo-i 
Walkers  Mt.  and  the  Peak  Hills  (near  Peak  Creek  Valley):  F,  fault;  a,  Lower  Silurian 
limestone ;  ft,  Upper  Silurian  ;  c,  Devonian ;  d,  Subcarboniferous,  with  coal  beds. 

As  shown  in  the  above  sections  (Figs.  206-209),  tLo 
anticlines,  instead  of  remaining  in  regular  rounded  ridges 
with  synclinal  valleys  between,  such  as  the  flexing  of  the 
strata  might  make,  have  been  to  a  great  extent  worn  away, 
or  modeled  into  new  ridges  and  valleys,  by  the  action  of 
waters  during  subsequent  time  ;  and  often  what  was  the 
top  of  a  fold  is  now  the  bottom  of  a  valley.  The  figures 
on  pages  135,  136  illustrate  still  further  the  condition  of 
folded  strata  after  denudation.  Some  of  the  Appalachian 


214  DYNAMICAL   GEOLOGY. 

folds  were  probably  20,000  feet  in  height  above  the 
level  of  the  ocean,  or  would  have  had  this  height  if 
they  had  remained  unbroken,  while  in  fact  the  loftiest 
summits  now  are  less  than  5000  feet,  and  few  exceed 
3000  feet. 

The  following  are  some  of  the  general  truths  connected 
with  the  uplifts  and  metamorphisin  in  the  Appalachian 
region :  — 

1.  The  strike  of  the  strata,  and  the  courses  of  the  great 
flexures  and  faults,  are  approximately  northeast,  or  parallel 
to  the  Atlantic  border. 

2.  The  anticlines  generally  have  their  steepest  slope 
toward  the  northwest,  or  away  from  the  ocean.     This  is 
shown  in  Fig.  209 ;  and  in  Fig.  208  the  western  anticline 
is  actually  overthrown,  so  that  its  western  limb  is  carried 
beyond  the  perpendicular. 

3.  The   flexures  are  most  numerous  and  most  abrupt 
on  that  side  of  the  Appalachian  region  which  is  toward 
the  ocean,  and  the  folding  diminishes  in  intensity  west- 
ward.    There   is  seldom,  however,  a  gradual  dying  out 
westward,  the  region  of  disturbance  being  often  bounded 
on  the  west  by  one  or  more  of  the  great  fractures  and 
faults,  as  in  eastern  Tennessee. 

4.  The  consolidation  and  metamorphism  of  the  strata 
are  more  extensive   and   complete   to   the   eastward   (or 
toward  the  ocean)  than  to  the  westward. 

5.  The   change   of   bituminous   coal  to  anthracite,   by 
the  expulsion  of  volatile  ingredients,  was  most  complete 
where   the    disturbances   were  greatest ;    that  is,  in  the 
more  eastern  portions  of  the  coal  areas.     The  anthracite 
region  of  Pennsylvania  (see  map,  page  292)  owes  its  broken 
character  partly  to  the  uplifts  and  partly  to  denudation. 
To  the  westward  the  coal  is  first  semi-bituminous,  and 
then,    as   at   Pittsburg,    bituminous.      In   Rhode    Island, 
where  the  associated  rocks  are  partly  true  metamorphic  or 
crystalline  rocks,  and  the  disturbances  are  very  great,  the 
coal  is  an  extremely  hard  anthracite,  and  in  some  places 


CRUSTAL  MOVEMENTS. 


215 


is  altered  to  graphite  —  an  effect  which  may  be  produced 
in  ordinary  coal  by  the  heat  of  a  furnace. 

These  facts  lead  to  the  following  conclusions  :  — 

1.  The  movement  producing  these  vast  results  was  due 
to  lateral  pressure,  the  folding  having  taken  place  just  as 
it  might  in  paper  or  cloth  under  a  lateral  or  pushing 
movement. 

2.  The  pressure  was  exerted   at  right  angles   to   the 
courses  of  the  folds,  as  is  the  case  when  paper  is  folded 
in  the  manner  mentioned. 

3.  The  pressure  was  exerted  from  the  ocean  side  of  the 
Appalachians ;  for  the  results  in  foldings  and  metamor- 
phism  are  most  marked  toward  the  ocean. 

FIG.  211. 


trpturned  strata  of  the  west  slope  of  the  Elk  Mountains,  Colorado.    The  light-shaded  stratum, 
Jura-Trias ;  that  to  the  right  of  it,  Carboniferous  ;  that  to  the  left,  Cretaceous. 

4.  The  force  was  vast  in  amount. 

5.  The  force  was  slow  in  action  and  long  continued  — 
not  abrupt  or  paroxysmal,  as  when  a  wave  or  series  of 
waves  is  thrown  up  by  an  earthquake  shock  on  the  sur- 
face of  an  ocean.     For  the  strata  were  not  reduced  by  it 
to  a  state  of  chaos,  but  retain  their  stratification,  and  show 
comparatively  little   confusion,   even   in   the   regions   of 
greatest  disturbance  and  alteration. 

6.  The  action  of  the  force  was  attended  by  the  produc- 
tion of  heat.     For,  without  some  heat  above  the  ordinary 
temperature,  it  is  not  possible  to  account  for  the  consoli- 
dation and  crystallization  of  the  rocks. 

The  characteristic  features  of  mountain  structure  which 


216  DYNAMICAL   GEOLOGY. 

have  thus  been  illustrated  from  the  Appalachian  region, 
are  repeated,  with  variations  in  detail,  in  most  mountain 
regions.  Mountain  ranges  in  general  consist  of  masses  of 
strata  of  enormous  thickness,  folded  and  faulted  often 
with  great  complexity,  and  often  showing  intense  meta- 
morphism.  Fig.  33,  on  page  54,  illustrates  a  very  com- 
plex fold  in  the  Alps.  Fig.  211  is  an  illustration  of 
folded  and  overturned  strata  in  the  Rocky  Mountain 
region. 

Moreover,  the  unsymmetrical  character  which  has  been 
pointed  out  in  the  descriptions  of  Appalachian  structure, 
is  generally  more  or  less  strongly  marked  in  other  moun- 
tain ranges.  The  flexures  are  in  general  more  numerous 
and  steeper,  and  metamorphism  and  igneous  eruptions 
more  extensive  on  one  side  than  on  the  other ;  and  the 
flexures  themselves  are  very  commonly  inequilateral. 

Process  of  Formation  of  Mountain  Ranges. 

A  Geosyncline,  or  Downward  Bend  of  the  Crust,  the 
First  Step  in  Ordinary  Mountain-making.  —  In  the  making 
of  the  Appalachians,  there  was  first  a  slowly  progressing 
subsidence ;  it  began  in,  or  before,  the  Cambrian  era,  and 
continued  in  progress  until  the  Carboniferous  era  closed. 
As  the  trough  deepened,  deposits  of  sediment,  and  some- 
times of  limestone,  were  made,  that  kept  the  surface  of 
the  region  near  the  water  level ;  and,  when  the  trough 
reached  its  maximum,  there  were  30,000  to  40,000  feet  in 
thickness  of  stratified  rock  in  it  (page  317),  and  this, 
therefore,  was  the  depth  of  the  trough.  The  Taconic 
Mountains  began  in  a  similar  subsidence,  and  at  the  same 
time ;  and  the  trough  was  kept  full  with  deposits  as  it 
progressed ;  but  it  reached  its  maximum,  or  the  era  of 
catastrophe,  at  the  close  of  the  Lower  Silurian.  The  his- 
tory of  most  other  mountain  ranges  is  similar  to  these. 

The  subsidence  in  such  a  geosyncline  has  been  attrib- 
uted by  some  geologists  to  the  weight  of  the  accumulating 


CRUSTAL  MOVEMENTS.  217 

sediments,  in  accordance  with  the  principle  of  isostasy ; 
but  the  gradual  downward  bending  of  the  crust  may  be 
better  explained  as  a  result  of  the  same  lateral  pressure  to 
which  the  final  catastrophe  is  due. 

The  Bottom  of  %the  Geosyncline  weakened  by  the  Heat 
rising  into  it  from  below.  —  As  planes  of  equal  temperature 
within  the  earth  are  approximately  parallel  to  the  sur- 
face, the  accumulation  of  sedimentary  beds  in  a  sinking 
trough  would  occasion,  as  Herschel  long  since  urged,  the 
corresponding  rising  of  heat  from  below,  so  that,  with 
30,000  feet  of  such  accumulations,  a  given  isothermal 
plane  would  be  raised  30,000  feet.  Under  such  an  ac- 
cession of  heat,  the  rocks  at  the  bottom  of  the  trough 
would  be  greatly  weakened.  If  the  lower  surface  of  the 
crust  dipped  down  six  or  eight  miles  into  a  zone  of  plas- 
tic material  beneath  it,  it  would  be  actually  melted  off. 
Even  on  the  supposition  that  the  earth  is  completely 
solid,  and  no  subcrustal  plastic  layer  exists,  the  weak- 
ening of  the  geosyncline  by  the  rise  of  the  isothermal 
planes  would  be  no  less  real.  For,  in  the  formation 
of  the  geosyncline,  a  great  thickness  of  anhydrous,  crys- 
talline, refractory  rock  would  be  replaced  by  water- 
loaded  sediments  capable  of  suffering  aqueo-igneous 
fusion  (or  at  least  pastiness)  at  a  comparatively  low  tem- 
perature. The  lateral  pressure,  acting  against  a  trough 
thus  weakened,  would  end  in  causing  a  collapse  —  that  is, 
a  catastrophic  crushing  of  the  trough,  and  a  folding  of  the 
stratified  beds  within  it.  And  with  this  the  shaping  of 
the  mountain  range  would  begin. 

Character  of  the  Mountain  thus  made.  —  Under  such  cir- 
cumstances, the  stratified  rocks  lying  in  the  geosyncline 
or  trough  would  be  folded,  profoundly  broken,  shoved 
along  fractures,  and  pressed  into  a  narrower  space  than 
they  occupied  before.  The  flexures  were  flexures  in  the 
strata  that  filled  the  geosyncline,  not  in  the  subjacent  mass. 
They  were  simply  anticlines  and  synclines,  as  distinguished 
from  geanticlines  and  geosyiiclines  (page  55).  They  be- 


218  DYNAMICAL  GEOLOGY. 

came  unequal-sided,  as  represented  on  pages  212,  213,  and 
the  mountain  range  itself  inequilateral  (pages  214,  216), 
because  there  was  a  pushing  side  in  the  mountain-making, 
the  force  coming  mainly  from  one  direction  (the  oceanic,  in 
the  case  of  the  Appalachians).  Such  a  mountain  range, 
begun  in  a  geosyncline,  and  ending  in  a  catastrophe  of  dis- 
placement and  upturning,  has  been  named  a  synclinorium. 
(The  word  is  from  the  Greek  words  from  which  syncline 
is  derived,  and  o/jo?,  mountain.) 

On  the  side  away  from  the  chief  source  of  movement, 
and  beyond  the  profoundest  faults,  the  elevations  that 
have  taken  place  have  commonly  made  vast  plateaus  of 
nearly  horizontal  beds,  like  the  Cumberland  Mountain 
region  of  Tennessee  and  its  continuation  through  western 
and  northern  Pennsylvania  to  the  Catskill  Mountain 
plateau  of  southern  New  York,  on  the  outskirts  of  the 
Appalachian  range.  In  such  elevated  areas,  several  thou- 
sands of  feet  above  the  sea  level,  and  of  wide  extent, 
running  waters  have  had  their  opportunity  for  sculptur- 
ing, and  have  thus  made  some  of  the  most  majestic 
mountain  groups  of  ridges  and  peaks  in  the  world.  In 
Tennessee,  the  region  of  great  folds  and  faults  directly 
east  of  the  Cumberland  plateau  was  at  first,  beyond  doubt, 
of  far  greater  height  than  the  plateau;  but,  owing  to  the 
vast  amount  of  fracturing,  as  well  as  the  less  resistant 
character  of  the  rocks,  denudation  has  finally  made  it 
lower,  and  it  is  now  the  "  Valley  of  East  Tennessee," 
while  the  plateau  is  "  Cumberland  Mountain."  Not  less 
was  the  denudation  in  front  of  the  Catskill  plateau. 

Metamorphism  and  other  Attendant  Effects.  —  The  heat 
developed  through  the  transformation  of  motion,  added 
to  that  rising  into  the  strata  from  below,  would  pro- 
duce all  the  consolidation  and  crystallization  —  that  is, 
all  the  metamorphism  —  which  has  been  in  any  case 
observed,  and  on  a  scale  as  vast  as  that  of  the  mountain 
range  so  developed.  It  gives  a  full  explanation,  there- 
fore, of  the  origin  of  regional  metamorphism. 


CBTJSTAL  MOVEMENTS.  219 


The  heat  might  be  sufficient  in  some  parts  to  reduce  a 
rock  to  a  plastic  state,  and  so  obliterate  all  its  original 
bedding.  One  result  of  this  would  be  tg  make  a  massive 
rock,  like  granite,  in  place  of  gneiss  or  other  schistose 
kind;  and  another  result,  if  the  overlying  rocks  were 
fractured,  and  so  fissures  opened  down  to  the  plastic  rock, 
would  be  to  fill  the  fissures  with  the  plastic  rock,  making 
dikes  of  granite,  or  of  other  material,  according  to  the 
kind  of  rock  so  fused.  It  might  possibly  give  a  long  core, 
or  central  mass,  of  granite  to  a  mountain  range  —  a  con- 
dition of  the  Sierra  Nevada  which  has  been  attributed  by 
some  to  this  cause. 

Slaty  Cleavage  ;  Jointed  Structure.  —  Slaty  cleavage  has 
been  proved  by  experiments  to  result  whenever  fine- 
grained material  is  subjected  to  pressure ;  and  to  be  due 
to  the  flattening  of  all  compressible  particles,  and  the 
arranging  of  all  flat  grains  in  planes  at  right  angles  to 
the  pressure.  Since  it  occurs  in  fine-grained  rocks  that 
have  been  upturned  or  flexed,  and  since  it  is  parallel  to 
the  axes  of  the  folds,  the  pressure  producing  the  upturn- 
ing or  flexure  and  the  concomitant  mountain-making,  has 
been  generally  the  cause.  The  cleavage  conforms  to  the 
bedding  whenever  the  bedding  is,  as  a  consequence  of  the 
upturning,  at  right  angles,  or  nearly  so,  to  the  pressure. 

A  jointed  structure,  on  the  large  scale  observed  in  many 
regions,  has  been  another  result  of  the  slow  uplifting  or 
flexing  action  from  lateral  pressure.  Sometimes  a  region 
thus  disturbed  is  traversed  by  a  single  series  of  nearly 
parallel  joints ;  in  other  cases  two  such  series  of  joints 
are  produced  nearly  at  right  angles  to  each  other  (a 
structure  which,  as  shown  by  Daubree,  may  be  due  to 
torsion  of  the  strata).  Sometimes  joints  are  produced  in 
various  directions,  no  system  being  traceable. 

Geanticlines  in  Mountain-making.  —  In  the  movements 
of  the  earth's  crust  there  would  necessarily  be  upward 
as  well  as  downward  flexures,  —  that  is,  geanticlines  as 
well  as  geosynclines.  During  the  progress  of  the  Appa- 


220  DYNAMICAL   GEOLOGY. 

lachian  geosyncline,  geanticlines  were  in  progress  both 
east  and  west  of  the  subsiding  area.  In  the  eastern 
geanticline,  the  Atlantic  border  from  New  York  south- 
westward  beyond  Virginia  emerged,  and  continued  appar- 
ently to  be  dry  land  until  the  middle  of  the  Cretaceous. 
The  western  geanticline  —  the  Cincinnati  uplift  —  made 
two  large  islands  in  the  mediterranean  sea  which  then 
covered  much  of  the  continent,  one  in  the  region  of 
Cincinnati,  the  other  in  Tennessee.  The  present  altitude 
of  the  Appalachians,  in  spite  of  the  enormous  denudation 
they  have  suffered,  is  probably  due  in  part  to  a  geanticlinal 
movement  which  lifted  the  eastern  border  of  the  continent 
in  the  Tertiary  era. 

The  Rocky  Mountains,  in  the  Cretaceous  era,  within  the 
area  of  the  United  States,  were  10,000  feet  below  their 
present  level,  the  sea  covering  large  areas  over  what  is  now 
the  summit  region  (page  376).  They  were  raised  as  a 
whole  during  the  Tertiary,  and  it  must  have  been  through 
a  broad  and  gentle  geanticline.  While  the  Tertiary  moun- 
tain ranges  were  in  progress,  the  part  of  the  force  not  ex- 
pended in  producing  them  appears  to  have  carried  forward 
an  upward  bend,  or  geanticline,  of  the  vast  Rocky  Moun- 
tain region  as  a  whole. 

As  a  mountain  range  resulting  from  the  crushing  of  a 
geosyncline  is  called  a  synclinorium  (page  218),  a  region 
raised  to  a  high  altitude  by  a  geanticlinal  movement  may 
be  called  an  anticlinorium.  The  same  region  inay  expe- 
rience both  kinds  of  movement  in  the  course  of  its  history. 
The  Rocky  Mountain  region  as  a  whole  is  an  anticlino- 
rium. Many  of  its  component  parts  are  typical  syncli- 
noria. 

The  movements  over  the  continents  in  Cenozoic  time 
were  characterized  in  general  by  the  vast  areas  of  the  re- 
gions affected.  Great  geanticlinal  movements  in  the  Ter- 
tiary gave  to  some  of  the  great  mountain  chains  a  large 
part  of  their  altitude.  Areas  of  continental  extent  were 
involved  in  the  oscillations  of  level  which  characterized 


CRUSTAL   MOVEMENTS.  221 

the  Quaternary.  If  Darwin's  view  of  the  formation  of 
atolls  is  true  (see  page  103),  the  coral  island  subsidence 
—  affecting  an  area  in  the  Pacific  over  5000  miles  in  its 
longer  diameter  —  may  well  have  been  the  counterpart  of 
the  vast  geanticlmal  movements  over  the  continents  in  the 
later  Tertiary  and  early  Quaternary. 

Eruptions  of  Igneous  Rock.  —  The  great  fractures  as- 
sociated with  mountain-making  movements  have  often 
extended  down  to  regions  of  molten  rock,  and  given  pas- 
sage for  eruptions.  This  seems  to  have  been  especially 
true  in  connection  with  the  great  geanticlinal  movements 
of  later  geological  time.  The  greatest  lava  floods  of  which 
we  have  evidence,  as  those  of  the  Deccan  and  of  the  north- 
western United  States  (page  189),  belong  to  late  Meso- 
zoic  or  to  Ceriozoic  time. 

Such  are  the  general  steps  of  progress,  and  their  expla- 
nations, according  to  that  theory  of  mountain-making 
which  attributes  the  movement  to  a  lateral  thrust  in  the 
earth's  crust  as  a  result  of  contraction  in  cooling.  The 
universality  of  system  in  the  features  of  continents  and 
the  characters  of  mountains  has  as  yet  no  other  probable 
explanation. 

To  obtain  an  adequate  idea  of  the  slow  progress  of  the 
earth  in  the  making  of  its  mountains,  it  is  necessary  to  re- 
member that  orogenic  disturbances  have  taken  place  only 
after  immensely  long  periods  of  quiet  and  gentle  oscilla- 
tions. After  the  beginning  of  the  Cambrian,  the  first  pe- 
riod of  disturbance  in  North  America  of  special  note  was 
that  at  the  close  of  the  Lower  Silurian,  in  which  the 
Taconic  Mountains  were  finished ;  and,  if  time,  from  the 
beginning  of  the  Cambrian  to  the  present,  included  only 
48  millions  of  years  (page  444),  the  interval  between  the 
beginning  of  the  Cambrian  and  the  uplift  and  metamor- 
phism  of  the  Taconic  Mountains  was  at  least  20  millions 
of  years.  Another  epoch  of  disturbance  was  that  at  the 
close  of  the  Carboniferous  era,  in  which  the  rocks  of  the 


222 


DYNAMICAL   GEOLOGY. 


Appalachian  range  were  folded  up ;  on  the  above  estimate 
of  the  length  of  time,  it  occurred  about  36  millions  of 
years  after  the  commencement  of  the  Cambrian ;  so  that 
the  Appalachians  were  at  least  36  millions  of  years  in  mak- 
ing, the  preparatory  subsidence  having  begun  as  early  as 
the  beginning  of  the  Cambrian.  Thus,  whatever  the 
mountain-making  force,  an  exceedingly  long  time  was  re- 
quired in  order  to  accumulate  a  sufficient  amount  to  pro- 
duce a  general  yielding  and  plication  or  displacement  of 
the  beds,  and  start  a  new  range  of  prominent  elevations 
over  the  earth's  crust. 


PAKT    IV.  — HISTOEICAL   GEOLOGY. 


HISTORICAL  GEOLOGY  treats  of  the  order  of  succession 
in  the  strata  of  the  earth's  crust,  and  of  the  changes  that 
were  going  on  during  the  formation  of  each  bed  or  stratum 
—  that  is,  of  the  changes  in  the  oceans  and  the  land ;  of 
the  changes  in  the  atmosphere  and  climate  ;  of  the  changes 
in  the  plants  and  animals.  In  other  words,  it  is  an  his- 
torical view  of  the  events  that  took  place  during  the 
earth's  progress,  derived  from  the  study  of  the  successive 
rocks.  It  is  sometimes  called  stratigraphical  geology;  but 
this  term  properly  denotes  only  a  description  of  the  nature 
and  arrangement  of  the  earth's  strata. 

It  has  already  been  explained  that  the  rocks  of  the 
earth's  crust  are  historical  records  as  to  the  past  condi- 
tions of  the  earth's  surface.  In  order  that  the  records 
may  afford  an  intelligible  history,  there  must  be  some  way 
of  arranging  them  in  their  proper  order;  that  is,  in  the 
order  of  time.  The  determination  of  this  order  is  one  of 
the  first  things  before  the  geologist  in  his  examination  of 
a  country. 

Many  difficulties  are  encountered. 

1.  The  strata  of  the  same  period  —  called  equivalent 
strata,  because  approximately  equivalent  in  age  —  differ, 
even  on  the  same  continent.  Sandstones  and  shales  were 
often  forming  along  the  Appalachians  in  Pennsylvania  and 
Virginia,  when  limestones  were  in  progress  over  the  Missis- 
sippi Valley.  The  Cretaceous  formation  in  England  con- 

223 


224 


HISTORICAL   GEOLOGY. 


tains  thick  strata  of  chalk;  but  in  eastern  North  America 
the  same  formation  exists  without  any  chalk. 

2.  When  rocks  have  been  forming  in  one  region,  there 
have  been  none  in  progress  in  many  others.     Hence  the 
series  of  strata  serving  as  records  of  geological  events  is 
nowhere  perfect.     In  one  country  one  part  may  be  very 
complete ;  in  another,  another   part ;  and  all  have  their 
long  blanks  —  that  is,  large  parts  of  the  series  entirely 
wanting.     In  New  York  and  the  states  west  to  the  Missis- 
sippi, there  is  only  part  of  the  lower  half  of  the  series. 
In  New  Jersey  there  is  part  of  the  lower  half  and  part  of 
the  upper  half,  with  wide  breaks  between.     Over  a  large 
part  of   northern  New  York  there   exist   only  the  very 
earliest  of  rocks. 

3.  The  rocks  of  a  country  are  to  a  great  extent  cov- 
ered with  earth  or  soil,  so  that  they  can  be  examined  only 
at  distant  points. 

4.  The  strata,  in  many  regions,  have  been  displaced, 
folded,  fractured,  faulted,   and    even  crystallized   exten- 
sively, adding  greatly  to  the  difficulties  in  the  way  of  the 
geological  explorer. 

The  following  are  the  methods  to  be  used  in  determin- 
ing the  true  order  of  arrangement :  — 

(1)  In  sections  of  the  rocks  exposed  to  view  in  the  sides 
of  valleys  or  ridges,  the  order  of  superposition  should  be 
directly  studied,  and  each  stratum  traced,  as  far  as  possi- 
ble, through  all  the  exposed  sections. 

When,  through  large  intervals,  a  covering  of  soil  or 
water  prevents  the  tracing  of  the  beds,  other  means  must 
be  used. 

The  order  of  superposition,  when  not  directly  observ- 
able, may  often  be  inferred  by  observation  of  strikes  and 
dips  at  the  various  accessible  outcrops.  For  instance,  a 
stratum  dipping  east  must  underlie  another  stratum  with 
the  same  dip  whose  outcrop  is  farther  east  (unless  the 
strata  have  been  disturbed  by  faults  or  overturned  folds). 

The  validity  of  the  criterion  of  superposition  is  self- 


HISTORICAL   GEOLOGY.  225 

evident.  The  overlying  stratum  must  be  newer  than  the 
underlying.  But  it  is  obvious  that  this  criterion  is  only 
applicable  within  a  single  district.  For  the  comparison 
of  the  age  of  rocks  in  different  regions,  some  other  means 
are  necessary. 

(2)  The  aspect  or  composition  of  the  rock  may  help  to 
determine  which  strata  are  identical.     But  this  method 
should  be  used  with  great  caution,  for  the  reason  already 
stated — namely,  that  rocks  made  at  the  very  same  time  may 
be  widely  different;  and,  conversely,  those  made  in  very 
different  periods  may  look  precisely  alike  in  color  and 
texture.     Within  a  small  area,  the   resemblance   of   the 
rocks  at  two  or  more  outcrops  may  often  be  satisfactory 
proof   that  they  are  really  parts  of   the  same  stratum. 
But  the  value  of  this  test  diminishes  rapidly  as  the  dis- 
tance increases.     In  one  class  of  cases,  the  character  of  a 
rock  affords  unquestionable  evidence  in  regard  to  its  age. 
A  rock  including  fragments  of  some  other  rock  is  neces- 
sarily later  than  that  other  rock. 

(3)  Fossils  afford  the  most  generally  applicable  means 
of  determining  the  age  of  rocks.     This  is  so  because  of  the 
fact,  already  mentioned,  that  the  fossils  of  an  epoch  are 
'very  similar  in  genera  —  if  not  also  in  species  —  the  world 
over ;   and  those  of  different  epochs  are  different.     The 
geologist,  by  studying  the  fossils  of  the  several  beds  at  any 
locality,  learns  what  kinds  are  characteristic  of  each  bed, 
and  the  order  of  succession.     Then,  by  comparing  the  beds 
of  different  localities,  he  ascertains  whether  any  are  essen- 
tially alike  in  species,  and  therefore  of  like  age  or  period ; 
and  from  this  determination  he  continues  further  his  study 
of  the  order  of  succession.    By  pursuing  this  course,  for  all 
accessible  localities  in  different  countries,  geologists  have 
ascertained  the  characteristic  kinds  of  fossils  for  the  suc- 
cessive strata  through  the  long  series  of  formations ;  and 
the  lists  which  have  been  thus  made  serve  for  the  identifi- 
cation of  strata  in  widely  distant  regions.    By  a  comparison 
of  fossils  it  was  proved  that  the  Cretaceous  formation  exists 


226  HISTORICAL  GEOLOGY. 

in  eastern  North  America,  although  there  is  no  chalk  to  be 
found  there.  In  the  same  manner,  the  equivalents  in 
America  of  the  principal  subdivisions  of  the  rock  series 
of  Great  Britain  and  Europe,  Asia,  and  even  Australia,  are 
approximately  ascertained;  for  this  means  of  determination 
is  a  universal  one,  applying  to  the  equivalency  of  rocks 
in  different  hemispheres  as  well  as  those  on  the  same 
continent. 

This  method  has  its  uncertainties.  One  continent  may 
have  received  part  of  its  species  by  immigration  from 
another  long  after  their  first  appearance  in  that  other ;  and 
species  may  have  survived  in  one  continent  long  after  they 
have  become  extinct  in  another.  Moreover,  especially  in 
the  later  geological  periods,  the  progress  of  evolution 
seems  to  have  been  more  rapid  in  some  regions  than  in 
others.  The  mammalian  fauna  of  Australia  at  present 
consists  almost  exclusively  of  Marsupials  and  Monotremes. 
In  a  former  geological  period,  the  same  was  true  of  Europe 
and  North  America.  Other  continents  have  apparently 
outstripped  Australia  in  the  march  of  evolution.  Again, 
there  are  doubts  arising  from  the  fact  that,  in  any  period, 
the  life  of  one  locality,  even  of  marine  animals,  is  very 
different  from  that  of  another,  on  account  of  differences* 
in  depth  or  purity  of  waters,  muddy  or  rocky  bottom,  and 
temperature  ;  and  the  range  of  terrestrial  and  fresh-water 
species  is  generally  more  local,  and  their  value  as  criteria 
of  age  accordingly  less,  than  that  of  marine  species.  The 
removal  of  all  doubts,  and  the  determination  of  the  exact 
parallelism  of  the  minor  subdivisions  of  the  geological 
series  in  different  continents  or  distant  parts  of  the  same 
continent,  are  not  to  be  looked  for.  Yet,  by  proceeding 
with  care,  and  using  not  isolated  facts,  but  the  whole 
range  of  evidence  afforded  by  the  fossils,  animal  as  well 
as  vegetable,  the  general  chronological  order  may  be  deter- 
mined with  a  satisfactory  degree  of  approximation. 

The    chronological    order    of   events    recorded   in    the 
various  strata  being  determined  by  the  methods  already 


HISTORICAL  GEOLOGY.  227 

explained,  it  becomes  possible  to  divide  geological  time 
into  a  series  of  ages,  each  of  which  is  characterized  by 
a  particular  stage  in  the  earth's  progress,  and  particularly 
in  the  evolution  of  life.  The  progress  of  the  earth's  his- 
tory, like  that  of  human  history,  has  been  continuous,  the 
idea  characteristic  of  one  age  being  always  foreshadowed 
in  the  previous  age.  The  boundaries  of  the  various  aeons, 
eras,  periods,  and  epochs  recognized  in  geological  history 
are  therefore  necessarily  in  some  degree  arbitrary.  In 
many  cases  a  great  and  relatively  rapid  geographical 
change,  as  the  elevation  of  a  range  of  mountains,  serves 
as  a  time  boundary ;  and  such  changes  are  generally  indi- 
cated, at  least  in  the  more  disturbed  areas,  by  unconf  orma- 
bility  in  the  strata. 

Geological  time  is  thus  divided  into  four  aeons  :  — 

1.  In  the  rocks  of  the  earliest  aeon,  only  doubtful  traces 
of  life  are  found.     For  a  long  time  after  the  formation  of 
the  earth's  crust,  the  high  temperature  must  have  ren- 
dered the  existence  of  life  impossible.     Before  the  close 
of  the  aeon,  some  low  forms  of  vegetable  and  animal  life 
doubtless  appeared.     But  the  rocks  are  in  general  more 
or  less  strongly  metamorphic;  and  whatever  fossils  they 
may  once  have  contained,  have  been  entirely  destroyed,  or 
left  in  condition  doubtfully  recognizable.     This  aeon  is 
called  Archcean  time,  from  the  Greek  ap%tj,  beginning.     It 
may  be  considered  the  earth's  prehistoric  age. 

2.  The  rocks  of  the  next  aeon  reveal  the  fossil  remains 
of  an  abundant  fauna  and  flora.     In  the  early  part  of  the 
aeon,  the  animals  were  exclusively  marine  Invertebrates. 
Before  the  close  of  the  time,  however,  Insects,  Fishes,  and 
Amphibians  became  abundant,  and  a  few  Reptiles  made 
their  appearance  in  the  closing  period.     At  first,  the  plants 
were  only  Seaweeds  ;  but  plants  of  higher  grade  appeared 
later,  and  the  closing  era  was  characterized  by  a  luxuriant 
development    of    Acrogens    and    Gymnosperms.      Birds, 
Mammals,  and  Angiosperms  were  entirely  wanting.     This 
aeon  is   called  Paleozoic  time,  from   the   Greek  T 


228 


HISTORICAL   GEOLOGY. 


ancient,  and  £&>?;,  life.     It  represents  the  earth's  ancient 
history. 

3.  The  next  aeon  is  characterized  by  the  immense  de- 
velopment of  reptilian  life,  the  class  of  Reptiles  showing 
a  greater  number  of  species  and  of  ordinal  types,  greater 
size,  and  higher  grade  of  organization,  than  ever  before  or 
after.     Birds  and  Mammals  made  their  first  appearance, 
but  attained  only  a  feeble  development.     Among  plants, 
Gymnosperms  were  predominant  in  the  early  part  of  the 
aeon,  but  Angiosperms  became  abundant  in  its  closing  era. 
This  aeon  is  called  Mesozoic  time,  from  the  Greek  /-te'o-o?, 
middle,  and  £0)77,  life.     It  represents  the  earth's  mediaeval 
history.     It  may  fitly  be  called  the  Age  of  Reptiles. 

4.  The  last  *eon  is  characterized  by  the  great  develop- 
ment of  Mammals  among   animals  and  of  Angiosperms 
among  plants.     In  the  latter  of  the  two  eras  into  which 
it  is  divided,  Man  himself  appeared  as  the  crown  of  the 
animate  creation.     With  the  beginning  of  this  aeon,  we 
find   species   introduced   which   have    continued    to    the 
present  time,  whereas  the  species  of  the  former  aeons  are 
all  (or  nearly  all)  extinct.     This  aeon  is  called   Cenozoic 
time,  from   the  Greek  KCUVOS,  recent,   and   far),  life.     It 
represents  the  earth's  modern  history. 

Extensive  upturnings  of  rocks  in  various  regions  mark 
the  close  of  the  three  earlier  aeons,  so  that,  in  many  locali- 
ties, strongly  marked  unconformabilities  separate  the  rocks 
of  successive  aeons  from  one  another.  In  North  America, 
the  elevation  of  the  Appalachian  mountain  system  marks 
the  close  of  Paleozoic  time,  and  the  elevation  of  the 
Laramide  mountain  system,  the  close  of  Mesozoic  time. 

Paleozoic  time  is  divided  into  five  eras,  Mesozoic  time 
into  three,  and  Cenozoic  time  into  two. 

The  eras  of  Paleozoic  time  are  the  following  :  — 

1.  Cambrian.  —  In  this  era,  the  animals  were  exclusively 
marine  Invertebrates,  and  the  plants  were  exclusively  Sea- 
weeds. 

2.  Lower  Silurian,  or  Ordovician,  —  In  this  era  appeared 


HISTORICAL   GEOLOGY.  229 

a  few  Fishes,  Insects,  and  terrestrial  plants  —  a  sort  of 
prophecy  of  the  life  of  succeeding  eras.  But  the  land 
areas  were  as  yet  small,  and  the  development  of  terrestrial 
life  insignificant.  The  Cambrian  and  Lower  Silurian  eras 
may  be  called  the  Age  of  Invertebrates. 

3.  Upper  Silurian. — In  this  era,  Fishes,  Insects,  and 
land  plants  became  more  abundant. 

4.  Devonian. — In  this   era,  Fishes  showed  a   further 
increase    in    number    of    species    and  diversity  of    type. 
Amphibians  seem  to  have   made  their  first  appearance. 
The  land  areas  became  more  extensive,  and  were  clothed 
in  part  with  a  forest  vegetation  consisting  chiefly  of  Aero- 
gens,  but  with  a  few  Gymnosperms.     The  Upper  Silurian 
and  Devonian  eras  may  be  called  the  Age  of  Fishes. 

5.  Carboniferous.  —  A    luxuriant    forest     and    swamp 
vegetation  of  Acrogens  and  Gymnosperms  furnished  the 
material  for  most  of  the  great  coal  beds  of  eastern  North 
America  and  of  Europe.     Amphibians  became  abundant, 
and  a  few  Reptiles  appeared  in  the  closing  period  of  the 
era.     The  Carboniferous  era  may  be  called  the  Age  of 
Acrogens,  or  the  Age  of  Amphibians. 

Paleozoic  time  may  be  divided  into  two  sections,  the 
Eopaleozoic  and  the  Neopaleozoic,  the  former  including  the 
first  two  eras,  and  the  latter  the  last  three.  They  are 
characterized,  respectively,  by  the  almost  complete  absence 
of  terrestrial  life  in  the  former,  and  its  considerable  de- 
velopment in  the  latter.  Extensive  upturnings  of  rocks, 
and  consequent  unconformability  in  many  regions,  mark 
the  transition.  In  eastern  North  America,  the  elevation 
of  the  Taconic  mountain  system  forms  a  well-defined  time 
boundary  between  the  two  sections  of  Paleozoic  time. 

The  eras  of  Mesozoic  time  are  the  following :  — 

1.  Triassic. — In  this  era,  Reptiles  first  became  abun- 
dant, and  the  earliest  Mammals  (probably  Monotremes) 
made  their  appearance. 

2.  Jurassic.  —  In  this  era,   Reptiles  became  still  more 
abundant,  and  presented  a  greater  diversity  of  type.     The 


230 


HISTORICAL   GEOLOGY. 


-<EONS.      ERAS. 


FIG.  212. 

AMERICAN  PERIODS.  FOREIGN  EQUIVALENTS. 


HISTORICAL   GEOLOGY. 


231 


ERAS. 


FIG.  212  (continued). 

AMERICAN  PERIODS.  FOREIGN  EQUIVALENTS. 


Keuper  and  Ehaetic 

Muschelkalk 
Bunter  Sandstein 


class  culminated  at  the  end  of  this  era,  or  at  the  beginning 
of  the  next.  Birds  made  their  first  appearance.  Gymno- 
sperms  were  the  dominant  type  of  vegetation. 

3.  Cretaceous.  —  The  appearance  of  Angiosperms  gave 
to  the  vegetation  a  modern  aspect.  Fishes  of  modern 
type  (Teleosts)  became  abundant. 

The  eras  of  Cenozoic  time  are  the  following  :  — 
1.  Tertiary.  —  In  this  era  there  is  still  no  evidence  of 
the  existence  of  Man.  The  Invertebrates  were  in  large 
part  of  species  which  still  exist,  but  the  Vertebrates  were 
all  of  extinct  species.  The  Tertiary  era  may  be  called  the 
Age  of  Mammals. 


232  HISTORICAL    GEOLOGY. 

2.  Quaternary.  —  Man  himself,  and  other  existing  spe- 
cies of  Vertebrates,  made  their  appearance.  The  era  may 
be  called  the  Age  of  Man. 

The  successive  strata  in  the  formations  of  an  era  are  very 
diversified  in  character,  limestones  being  overlain  abruptly 
by  sandstones,  conglomerates,  or  shales,  or  either  of  these 
last  by  limestones ;  and  each  may  be  very  different  from 
the  following  in  its  fossils.  These  abrupt  transitions  in 
the  strata  are  proofs  that  there  were  great  changes  at  times 
in  the  conditions  of  the  region  where  the  strata  were 
formed,  and  the  transitions  in  the  kinds  of  fossils  are  evi- 
dence of  great  destruction  at  intervals  in  the  life  of  the 
seas.  Such  transitions,  therefore,  naturally  divide  the 
eras  into  smaller  portions  of  time,  or  periods,  as  they  are 
called.  By  transitions  similar  in  kind,  but  not  so  great, 
periods  may  generally  be  subdivided  into  still  smaller 
parts,  or  epochs ;  and  even  the  epochs  often  admit  of  still 
more  minute  subdivision. 

The  preceding  summary  of  the  life  of  the  successive 
seons  and  eras  will  suggest  to  the  student  two  important 
generalizations. 

1.  There  has  been  a  continuous  approximation  to  the 
life  of  the  present  day,  as  shown,  through  all  geological 
time  by  the  increasing  number  of  classes  and  other  com- 
prehensive groups  identical  with  those  now  existing,  and, 
finally,  in  Cenozoic  time,  by  the  gradual  introduction  of 
species  that  still  survive. 

2.  There  has  been,  on  the  whole,  a  progress  from  lower 
to  higher  forms  of  life. 

These  facts  will  be  recognized  as  strikingly  in  harmony 
with  that  theory  of  the  origin  of  species  by  evolution,  or 
descent  with  modification,  which  is  generally  adopted  by 
the  naturalists  of  the  present  time.  The  subject  will  be 
discussed  more  fully  when  the  student  is  in  possession  of 
the  facts  in  some  degree  of  detail. 

The  aeons,  eras,  and  periods  recognized  in  American 
geology  are  exhibited  in  the  following  table :  — 


HISTORICAL   GEOLOGY. 
I.  ARCH  JEAN  TIME. 


233 


2, 


2. 


H.   PALEOZOIC  TIME. 

i.   Eopaleozoic  Section. 
Cambrian  Era. 

1.  Lower  Cambrian,  or  Georgian,  Period. 

2.  Middle  Cambrian,  or  Acadian,  Period. 

3.  Upper  Cambrian,  or  Potsdam,  Period. 

Lower  Silurian  Era. 

1.  Canadian  Period. 

2.  Trenton  Period. 

2.  Neopaleozoic  Section. 

Upper  Silurian  Era. 

1.  Niagara  Period. 

2.  Onondaga  Period. 

3.  Lower  Helderberg  Period. 


Devonian  Era. 

1.  Oriskany  Period. 

2.  Corniferous  Period. 

3.  Middle  Devonian,  or  Hamilton,  Period. 

4.  Upper  Devonian,  or  Chemung,  Period. 

3.    Carboniferous  Era. 

1.  Subcarboniferous  Period. 

2.  Carboniferous  Period. 

3.  Permian  Period. 


III.   MESOZOIC  TIME. 


1.  Triassic  Era. 

2.  Jurassic  Era. 

3.  Cretaceous  Era. 

1.  Tertiary  Era. 

1.  Eocene  Period. 

2.  Miocene  Period. 

3.  Pliocene  Period. 

2.  Quaternary  Era. 

1.  Glacial  Period. 

2.  Champlain  Period. 

3.  Recent  Period. 


IV.   CENOZOIC  TIME. 


AGE  OF 
INVERTEBRATES. 


AGE  OF  FISHES. 


AGE  OF  ACRO- 
GENS,  OR  AGE 
OF  AMPHIBIANS. 


AGE  OF  REPTILES. 


AGE  OF  MAMMALS. 


AGE  OF  MAN. 


234  HISTORICAL  GEOLOGY. 

The  ideal  section  on  pages  230,  231,  will  further  illus- 
trate the  succession  of  eras  and  periods,  and  will  also  in- 
dicate to  some  extent  the  European  (especially  British) 
equivalents  for  the  divisions  recognized  in  this  country. 

The  names  of  the  periods  in  the  first  part  of  the  section 
(those  of  the  Paleozoic)  are  mostly  derived  from  the 
names  of  American  rocks  or  localities.  The  names  in 
the  other  part  are  mostly  European,  as  the  series  of  rocks 
it  includes  (those  of  Mesozoic  and  Cenozoic  time)  is  more 
complete  in  Europe  than  in  America. 

It  will  be  observed  that  the  same  names  are  in  use  on 
both  continents  for  the  eras,  and  to  some  extent  for  the 
periods,  since  approximate  correlations  have  been  estab- 
lished for  the  larger  divisions  of  geological  time  all  over 
the  world.  It  is,  however,  impossible  to  establish  such 
correlations  in  regard  to  the  smaller  subdivisions.  Hence, 
the  names  of  periods  to  some  extent,  and  of  epochs  and 
minuter  subdivisions  universally,  differ  in  different  coun- 
tries and  even  in  different  parts  of  the  same  country. 
The  names  of  several  of  the  eras  are  derived  from  localities 
in  Great  Britain  —  a  region  in  which  the  series  of  forma- 
tions is  displayed  with  remarkable  completeness,  and  in 
which  the  study  of  stratigraphical  geology  was  first  devel- 
oped. In  somewhat  analogous  fashion,  the  American 
names  of  periods  and  epochs  in  the  Paleozoic  are  in 
great  part  derived  from  localities  in  the  State  of  New 
York  —  the  series  of  Silurian  and  Devonian  rocks  in  that 
state  being  remarkably  complete,  and  having  been  thor- 
oughly studied  in  the  beginning  of  geological  work  in 
this  country. 

The  map  on  page  235  represents  the  distribution  of 
the  rocks  of  the  different  ages,  as  surface  rocks,  over 
part  of  the  United  States  and  Canada.  The  areas  indi- 
cated by  the  different  kinds  of  shading  are  stated  on  the 
map.  The  areas  left  white  are  of  unascertained  or  doubt- 
ful age. 

Silurian  strata  may  underlie  the  Devonian,  and  both 


235 


236  HISTORICAL   GEOLOGY. 

Silurian  and  Devonian  may  underlie  the  Carboniferous. 
The  black  areas  of  the  Carboniferous  period  do  not,  there- 
fore, indicate  the  absence  of  Devonian  and  Silurian,  but 
only  that  the  Carboniferous  strata  are  the  surface  strata 
over  the  region. ' 

I.   ARCHAEAN  TIME. 

Archaean  time,  in  geology,  commences  with  the  earth 
already  a  solid  globe,  or  at  least  having  a  solid  crust ;  for 
the  conditions  of  only  such  a  globe  are  within  reach  of 
geological  investigation.  There  must  have  been  an  earlier 
time  in  which  the  earth  was  superficially  liquid,  and 
astronomy  leads  us  back  to  the  still  more  ancient  time 
when  the  earth  formed  a  part  of  the  nebula  of  which  the 
sun  is  the  central  residue. 

When  the  earth's  crust  was  first  formed,  its  temperature 
must  have  exceeded  2500°  F.  The  atmosphere  must  then 
have  contained  all  the  water  of  the  globe,  all  the  carbon 
(in  the  form  of  carbon  dioxide)  now  stored  in  solid  form 
as  coal  and  other  hydrocarbon  compounds  and  as  car- 
bonates, and  various  other  materials  which  have  since 
formed  solid  compounds.  When  the  ocean  was  first 
formed  by  condensation  from  the  atmosphere,  its  tem- 
perature may  have  been  as  high  as  500°  F.,  the  atmos- 
pheric pressure  being  still  perhaps  30  times  as  great  as  at 
present.  The  chemical  action  of  the  ocean  in  rock  de- 
struction and  rock  formation  must  then  have  been  very 
much  more  important  than  in  later  times.  Long  ages 
must  have  elapsed  before  the  earth  was  cool  enough  to 
permit  the  existence  of  the  lowest  organisms.  Archaean 
time  must  have  been  immensely  long. 

ROCKS:    KINDS   AND  DISTRIBUTION. 

1.  Distribution.  — Since  the  Archaean  era  commenced 
with  the  origin  of  the  earth's  crust,  Archaean  rocks  must 
extend  around  the  globe,  underlying  all  rocks  of  sub- 


ARCHAEAN   TIME. 


237 


sequent  ages,  and  furnishing  the  material  out  of  which 
most  of  these  later  rocks  have  been  made.  Over  by  far 
the  larger  part  of  the  surface  of  the  globe,  they  are 
concealed  from  view  by  subsequent  formations.  In  North 
America  they  are  surface  rocks  over  a  large  area  north  of 
the  Great  Lakes,  shaped  like  the  letter  V,  the  longer  branch 

FIG.  214. 


Map  showing  areas  of  Archaean  rocks  in  North  America. 

of  which  runs  northwest  to  the  Arctic  Ocean,  and  the 
shorter  northeast  to  Labrador.  The  large  white  area  on 
the  preceding  map,  in  what  is  now  British  America,  is  the 
portion  of  the  continent  here  referred  to.  Archaean  rocks 
also  appear  in  linear  areas  along  the  course  of  the  moun- 
tain chains  which  form  the  borders  of  the  continent.  The 
longest  of  these  areas  in  the  east  extends  (though  not 


238  HISTORICAL  GEOLOGY. 

> 

without  interruptions)  from  near  the  St.  Lawrence  to 
Georgia,  appearing  in  the  Green  Mountains  of  Vermont 
and  Massachusetts,  the  Highlands  of  New  York  and  New 
Jersey,  and  the  "Piedmont  belt"  of  the  South  Atlantic 
states.  Another  may  be  traced  from  Newfoundland 
through  Nova  Scotia  (with  a  submerged  interval)  to 
southeastern  Massachusetts.  In  the  west  the  most  exten- 
sive area  is  that  which  forms  the  "backbone"  of  the 
Rocky  Mountains.  An  isolated  area  appears  in  the 
Adirondacks,  and  another  south  of  Lake  Superior. 

In  Europe,  Archaean  rocks  are  in  view  in  the  great 
iron  regions  of  Sweden  and  Norway,  in  Bohemia,  and  in 
Scotland. 

2.  Kinds  of  Rocks.  —  The  rocks  are  mostly  crystalline 
rocks,   such   as   granite,  quartz    syenite,  gabbro,  gneiss, 
syenite   gneiss,   mica   schist,  hornblende   schist,   chlorite 
schist,  and  granular  limestone.     But  besides  these  there 
are  some  hard  conglomerates,  quartzites,  or  gritty  sand- 
stones, and  slates.    The  beautiful  iridescent  feldspar  called 
labradorite  (page  20)  is  a  common  constituent  of  some  of 
the  coarse  crystalline  rocks. 

An  abundance  of  iron  is  one  characteristic  of  the  beds. 

The  rocks  very  often  contain  hornblende,  an  iron-bearing 
mineral,  or  black  mica,  also  iron-bear- 
ing. There  are  in  some  regions  im- 
mense beds  of  iron  ore  (z,  i,  i,  in  Fig. 
215).  In  northern  New  York  the  beds 
are  100  to  200  feet  thick.  Similar 

iron  ore  b^s,  Essex  County,  jron  ore  deposits  occur  in  New  Jersey, 
in  Michigan,  south  of  Lake  Superior, 

and  in  Missouri.    Graphite  is  common  in  some  places,  and 

constitutes  2  to  30  per  cent  of  some  beds,  especially  of  the 

limestones. 

3.  Disturbance  and  Crystallization  of  the  Rocks.  —  The 
layers  of  gneiss  and  other  schistose  rocks,  with  the  in- 
cluded limestones,  are  nowhere  horizontal ;  but,  instead  of 
this,  they  dip  at  all  angles,  and  are  often  flexed  or  folded 


AKCILEAN  TIME. 


239 


in  a  most  complex  manner.  Fig.  216  represents  the  folded 
character  of  the  Archaean  rocks  of  Canada.  The  folded 
rocks  in  this  figure  are  overlain  by  beds  that  are  nearly  hori- 
zontal, which  belong  to  the  Cambrian  and  Lower  Silurian. 

Owing  to  the  dislocations  and  uplifts  which  the  rocks 
have  undergone,  giving  the  strata  often  a  nearly  vertical 
position,  the  iron  ore  beds  look  like  veins  (Fig.  215);  and 
even  the  strata  of  crystalline  limestone  have  often  a  similar 
veinlike  appearance. 

4.  Origin  of  the  Rocks. — The  indurated  sandstones, 
quartzites,  and  slates  are  of  course  ordinary  sediments  which 
have  undergone  more  or  less  of  metamorphism.1  The  same 
is  doubtless  true  of  some  of  the  gneisses  and  schists.  But 
a  considerable  part  of  the  gneisses  are  undoubtedly  derived 

FIG.  216. 


From  the  south  side  of  the  St.  Lawrence  in  Canada,  between  Cascade  Point  and  St.  Louis 
Rapids :  1,  Archaean  gneiss  ;  2,  Cambrian ;  3,  Canadian  ;  4  a,  6,  Trenton. 

from  igneous  rocks  (see  pages  30,  192).  Even  in  the 
case  of  those  schistose  rocks  which  have  been  derived  from 
stratified  rocks,  it  is  often  impossible  to  determine  whether 
the  foliation  corresponds  to  the  original  stratification,  or 
is  a  structure  superinduced  by  dynamic  metamorphism 
(page  195).  The  materials  which  have  crystallized  into 
the  Archaean  rocks  must  have  included  not  only  mechani- 
cal sediments,  but  also  chemical  deposits  (which,  as  re- 
marked on  page  236,  must  have  been  more  important  then 
than  in  later  times),  lava  flows,  and  tufa  beds.  Some,  at 
least,  of  the  iron  ore  beds  are  doubtless  metamorphosed 
chemical  deposits  (page  116). 

1  The  limestones,  quartzites,  slates,  and  other  rocks  whose  sedimentary 
origin  is  pretty  certain,  together  with  the  associated  igneous  rocks,  con- 
stitute the  Aljronkian  system  of  the  United  States  Geological  Survey. 
In  many  localities,  such  rocks  overlie  unconformabiy  the  more  highly 
crystalline  granites  and  gneisses. 


240  HISTORICAL   GEOLOGY. 

The  granites,  gabbros,  and  other  massive  rocks  are  prob- 
ably for  the  most  part  plutonic,  but  such  rocks  may  be  in 
some  cases  only  the  extreme  term  of  metamorphism. 

The  earliest  rocks  formed  in  Archaean  time  must  have 
resulted  from  the  solidification  of  the  molten  material  of 
the  globe.  But  it  is  unlikely  that  any  of  those  primitive 
rocks  are  anywhere  accessible  to  observation.  Most  of 
the  visible  Archaean  rocks  bear  evidence  of  a  derivative 
origin. 

It  is  probable  that,  in  the  course  of  Archaean  time,  there 
were  a  number  of  epochs  of  extensive  crustal  movements 
accompanied  by  metamorphism,  for  instances  of  uncon- 
formability  between  one  Archaean  rock  and  another  are 
frequent.  Since  a  strongly  marked  unconformability 
everywhere  separates  the  Archaean  from  later  formations, 
it  is  inferred  that  the  age  closed  with  an  epoch  of  very 
general  disturbance. 

Archaean  rocks  in  general  are  more  highly  crystalline 
than  those  of  later  formations  ;  yet  there  seems  to  be  no 
definite  lithological  criterion  which  will  distinguish  rocks 
of  that  age  from  metamorphic  and  plutonic  rocks  of  later 
times. 

LIFE. 

The  graphite,  abundant  in  some  beds  in  Canada,  is 
probable  evidence  of  the  existence  of  plants,  since  it  is 
known  that  in  later  times  graphite  has  been  formed  out 
of  vegetable  remains.  The  limestone  beds  suggest  the 
idea  that  there  was  present  either  vegetable  or  animal 
life  ;  for  almost  all  limestones  (see  page  99)  are  of  organic 
origin.  But  the  inference  in  both  cases  is  doubtful,  since 
both  graphite  and  limestone  may  have  been  formed  by 
purely  chemical  processes. 

No  distinct  fossil  plants  have  been  found,  though  gen- 
eral considerations  render  it  probable  that  plants  com- 
menced before  the  close  of  Archaean  time.  The  earliest 
plants  were  doubtless  Seaweeds.  No  vegetable  remains 


ARCHAEAN   TIME. 


241 


but  those  of  Seaweeds  are  found. in  the  overlying  Cam- 
brian strata. 

Fig.  217  represents  what  has  been  regarded  as  a  fossil 
animal,  and  named  Eozoon  Canadense.     It  is  supposed  to 
have  been  a  coral-like  mass  made 
by    Protozoans    of    the    class   of 
Rhizopods,    the    simplest   of    all 
kinds  of  animal  life.     The  dark 
layers  in  the  mass  are  supposed 
to  mark  the  position  of  the  soft 
part   of   the   animals,   while  the 
white  layers  are  supposed  to  be 
derived    from    their     calcareous 
skeleton.     The  supposed  animal 
nature    of    Eozoon   is,   however, 
probably  a  mistake.     Structures 
of  very  similar  appearance  have 
been   produced,  where  the   sup- 
position of  organic  origin  is  out 
of  the  question.     Still,  it  is  alto- 
gether  probable   that    Rhizopods   existed   in  the   waters 
before    the    close    of    the    Archaean    era,    and   that   they 
furnished  material  for  beds  of  limestone.     In  some  of  the 
less  strongly  metamorphic  rocks,  supposed  to  belong  to 
the  later  part  of  Archaean  times,  obscure  and  doubtful 
traces  of  animal  fossils  have  been  reported. 

GENERAL  OBSERVATIONS. 

The  large  area  of  Archaean  rocks  shown  on  the  map, 
page  237,  represents  the  main  portion  of  the  dry  land  of 
North  America  at  the  close  of  the  Archaean  age ;  for  it 
consists  of  rocks  made  during  the  age,  and  is  bordered  on 
its  different  sides  by  the  earliest  rocks  of  the  next  age. 
It  shows  the  outline,  approximately,  of  North  America 
as  it  appeared  when  the  Cambrian  era  opened.  It  was 
the  nucleus  around  which  in  the  course  of  time  the 
continent  grew.  The  smaller  Archaean  areas  appear  to 


Eozoon  Canadense. 


242  HISTORICAL  GEOLOGY. 

have  been  mountain  ridges  and  islands  in  the  great  con- 
tinental seas.  There  may  have  been  other  areas  of  dry 
land  at  the  close  of  Archaean  time,  which  were  subse- 
quently submerged  and  covered  by  later  formations. 

Since  the  Archaean  rocks  are  mainly  metamorphosed  sedi- 
ments, they  were  presumably  derived  in  large  degree  from 
the  waste  of  lands  already  emerged,  and  subject  to  ocean 
waves  and  other  denuding  agencies ;  but  of  the  situation 
and  boundaries  of  those  earliest  lands  we  have  no  definite 
knowledge. 

Europe  had  its  Archaean  lands  at  the  same  time  in  Scan- 
dinavia, Scotland,  Bohemia,  and  some  other  regions ;  and 
probably  each  of  the  other  continents  was  then  repre- 
sented by  larger  or  smaller  areas  of  dry  land. 

The  facts  to  be  presented  in  the  discussion  of  Paleozoic 
time  teach  that  the  great  but  yet  unmade  continents, 
although  small  in  the  amount  of  dry  land,  were  not  cov- 
ered by  the  deep  ocean,  but  only  by  comparatively  shallow 
seas.  They  were  already  outlined,  though  mostly  under 
water.  Portions  may  have  been  at  times  a  few  thousands 
of  feet  under  water,  but  in  general  the  depth  was  small 
compared  with  that  of  the  ocean. 

We  thus  gather  some  hints  with  regard  to  the  geography 
of  America  in  the  period  of  its  first  beginnings. 

The  outlines  of  the  northern  Archaean  area  on  the  map, 
page  237,  —  the  embryo  of  the  continent,  —  and  the  direc- 
tions of  the  other  Archaean  lands,  are  very  nearly  parallel 
to  the  coast  lines  of  the  present  continent.  The  Archaean 
lands,  both  in  North  America  and  Europe,  are  largest  in 
the  more  northern  latitudes. 

II.    PALEOZOIC  TIME. 

Paleozoic  time  is  divided  as  follows  :  — 
I.   EOPALEOZOIC  SECTION. 

1.  Cambrian  Era. 

2.  Lower  Silurian  Era. 


PALEOZOIC  TIME.  243 

II.   NEOPALEOZOIC  SECTION. 

1.  Upper  Silurian  Era. 

2.  Devonian  Era. 

3.  Carboniferous  Era. 

The  prefixes  used  in  forming  the  names  of  the  two  sec- 
tions are  derived,  respectively,  from  770)5,  dawn,  and  veo?, 
new.  The  boundary  of  the  two  sections  is  defined,  in 
eastern  North  America  and  western  Europe,  by  an  epoch 
of  mountain-making,  and  consequently  by  extensive  un- 
conformability  in  the  strata.  The  Eopaleozoic  section,  or 
Age  of  Invertebrates,  was  marked  by  a  rich  and  varied 
display  of  marine  invertebrate  life,  but  only  the  scantiest 
beginnings  of  Vertebrates  and  of  terrestrial  animals  and 
plants.  In  the  Neopaleozoic,  the  dry  lands  increased  in 
extent,  and  terrestrial  plants  and  animals  became  abun- 
dant. Vertebrates  increased  greatly  in  number  and 
variety,  Amphibians  making  their  appearance  in  the 
Devonian,  and  Reptiles  in  the  Carboniferous  era,  in 
addition  to  the  earlier  class  of  Fishes.  The  Upper  Silu- 
rian and  Devonian  are  called  the  Age  of  Fishes,  and  the 
Carboniferous  the  Age  of  Amphibians,  or  the  Age  of 
Acrogens. 

As  has  been  already  stated,  and  as  will  appear  more 
clearly  in  the  sequel,  the  American  continent  was  essenti- 
ally a  unit  in  its  evolution  through  all  geological  time. 
The  areas  of  rock-making  and  geographical  progress  in 
the  Paleozoic  were  accordingly  defined  by  the  conditions 
of  Archaean  geography.  The  map  of  North  America  at 
the  close  of  the  Archaean  (Fig.  214)  shows  the  shallow 
continental  sea  divided  into  three  parts  by  the  two  great 
Archaean  chains  of  islands  or  island  ridges,  following 
respectively  the  general  course  of  the  Appalachian  and 
the  Rocky  Mountain  chains.  Those  three  regions  —  the 
Interior  Continental  Sea,  the  Atlantic  Border,  and  the 
Pacific  Border  —  require  separate  consideration  in  tracing 
the  history  of  continental  growth.  The  Atlantic  Bor- 


244  HISTORICAL   GEOLOGY. 

der  and  the  Pacific  Border  regions  are  to  some  extent 
subdivided  by  the  shorter  Archaean  ridges  indicated  on 
the  map. 


I.  EOPALEOZOIC  SECTION. 

I.   CAMBRIAN  ERA. 

SUBDIVISIONS. 

The  name  Cambrian  is  derived  from  an  ancient  name 
of  Wales  —  a  region  in  which  the  rocks  of  this  era  were 
studied  by  Sedgwick  and  Murchison. 

It  includes  three  periods :  1,  LOWER  CAMBRIAN,  or 
GEORGIAN;  2,  MIDDLE  CAMBRIAN,  or  ACADIAN;  3,  UPPER 
CAMBRIAN,  or  POTSDAM. 

ROCKS:   KINDS  AND  DISTRIBUTION. 

The  Cambrian  rocks  usually  appear  along  the  borders 
of  the  Archaean  areas.  In  eastern  North  America  they 
border  the  Archaean  nucleus  of  the  continent,  and  the 
adjacent  Adirondack  island ;  they  appear  at  intervals 
along  both  sides  of  the  Appalachian  Archaean  area;  and 
they  occur  in  parts  of  the  troughs  between  the  more 
eastern  Archaean  ridges.  In  the  west  they  border  in 
various  places  the  Rocky  Mountain  Archaean  area  and 
various  Archaean  islands ;  they  are  laid  bare  in  the 
Colorado  Canon  by  the  deep  erosion  which  has  removed 
the  overlying  strata. 

The  rocks  include  sandstones,  shales,  conglomerates, 
and  limestones,  and,  in  some  localities,  quartzites,  slates, 
schists,  and  marbles,  resulting  from  the  metamorphism  of 
ordinary  stratified  rocks.  Many  of  the  beds  bear  evidence 
of  origin  in  very  shallow  water,  and  none  of  them  bear 
positive  evidence  of  deep-sea  origin. 

The  Potsdam  Sandstone  —  a  characteristic  rock  in  the 
vicinity  of  the  Adirondacks  —  belongs  to  the  Upper 
Cambrian. 


CAMBRIAN   ERA.  245 

The  beds  contain,  in  many  places,  ripple-marks  (Fig.  185, 
page  154);  mud-cracks  (Fig.  189);  layers  showing  the 
wind-drift,  and  the  ebb-and-flow,  structure  (Figs.  161, 
187);  worm  burrows  (Fig.  230);  and  occasionally  the 
tracks  of  some  of  the  animals  of  the  period. 

In  the  Taconic  Mountains  of  Vermont  and  Massa- 
chusetts, the  Cambrian  is  represented  by  a  great  quartzite 
formation,  with  intercalations  of  mica  and  hydromica 
schist. 

In  southeastern  Pennsylvania,  the  Lower  Cambrian  in- 
cludes a  great  thickness  of  quartzite  with  overlying  shales, 
or  slates,  and  limestone ;  and  besides  these  rocks  there 
are,  in  South  Mountain,  large  flows  of  basaltic  and  rhyo- 
litic  rocks. 

The  Keweenaw  formation,  south  of  Lake  Superior, 
consisting  of  many  thousands  of  feet  of  sandstone  strata, 
with  numerous  intercalations  of  dolerite,  felsite,  and  other 
igneous  rocks,  and  bearing  the  remarkable  deposits  of 
native  copper  for  which  the  region  is  famous  (page  201), 
is  very  probably  Cambrian,  though  it  contains  no  fossils, 
and  is  considered  by  some  geologists  to  be  older. 

In  Great  Britain  the  Cambrian  rocks  are  hard  sand- 
stones and  slates.  The  Lingula  Flags  are  included  in  the 
Upper  Cambrian.  They  are  most  extensively  in  view  in 
North  and  South  Wales  and  in  Shropshire. 

In  Lapland,  Norway,  Sweden,  and  Bohemia,  Cambrian 
strata  have  been  observed.  If  the  strata  of  later  date 
could  be  removed  from  the  continents,  we  should  probably 
find  the  Cambrian  beds  extensively  distributed  over  all 
the  continents. 

LIFE. 

These  most  ancient  of  fossiliferous  rocks  contain  no 
remains  of  terrestrial  life.  The  plants  of  the  period  that 
left  traces  in  the  rocks  were  all  Seaweeds.  Among  ani- 
mals, all  the  Invertebrate  subkingdoms  except  the  Tuni- 
cates  (which  are  destitute  of  skeletons)  were  represented 


246 


HISTORICAL  GEOLOGY. 


by  aquatic  species,  and  by  these  only  ;  there  is  no  evi- 
dence that  there  were  any  Vertebrates. 

It  is  remarkable  that  all  of  these  subkingdoms  were 
represented  already  in  the  Lower  Cambrian.  Moreover, 
among  the  Mollusks,  both  Lamellibranchs  and  Gastropods 
had  already  appeared.  In  the  Middle  and  Upper  Cam- 
brian the  species  are  mostly  different  from  those  of  the 


218 


FIGS.  218-221. 
219 


SPONGE:  Fig.  218,  Leptomitus  Zittelli.  —  ANTIIOZOANS:    Fig.   219,  Archseocyathus   pro- 
fundus  ;  220,  221,  Spirocyathus  Atlanticus. 

Lower  Cambrian,  but  they  belong  in  general  to  the  same 
groups.  The  most  important  step  of  progress  during  the 
Cambrian  is  the  introduction  of  the  class  of  Cephalopods 
—  the  highest  class  of  Mollusks  —  in  the  Upper  Cambrian. 
Sponges;  Coelenterates ;  Echinoderms.  —  Fig.  218  repre- 
sents one  of  the  Sponges,  and  Figs.  219-221  represent 
two  of  the  Corals  of  the  Lower  Cambrian.  The  Echino- 


CAMBRIAN  ERA. 


247 


derms   were    represented    chiefly   by    Cystoid    Crinoids. 
Fragments  of  Crinoidal  stems  are  not  uncommon. 

Molluscoids.  —  Remains  of  Brachiopods  are  abundant. 
The  Potsdam  sandstone  abounds  in  many  places  in  a 
shell  smaller,  in  general,  than  a  finger  nail,  related  to  the 
modern  Lingula  (Fig.  222).  Shells  of  genera  related  to 

FIGS.  222-225. 


FIGS.  226-229. 


226 


BRACHIOPODS:  Fig.  222,  Lingulella  prima;    223,  a,  Acrotreta  gemma,  x4;    224,  Orthis 
Highlanders  ;   225,  Orthisina  (Billingsella)  festinata. 

Lingula  are  so  characteristic  of  certain  strata  of  the  Cam- 
brian as  to  have  suggested  the  name  Lingula  Flags,  or 
Lingula  Sandstone. 

Mollusks.  —  Figs.  226-229  represent  some  of  the  Mol- 
lusks  of  the  Lower  Cam- 
brian. Especially  note- 
worthy were  the  forms 
referred  (though  not 
without  somewhat  of 
doubt)  to  the  Ptero- 
pods.  The  species  of 
that  group  at  present 
are  few  and  small.  In 
Cambrian  times  it  was 
probably  represented  by 
numerous  species,  some 
of  which  were  of  con- 
siderable size.  Some 
of  the  Cambrian  Ptero- 
pods  were  peculiar  in 
having  the  shell  pro- 
vided with  a  lid,  or  operculum.  The  Cephalopods  of  the 
Upper  Cambrian  include  both  forms  with  straight  shells 


LAMELLIBRANCH  :  Fig.  226,  Fordilla  Troyensis, 
x  5.  —  GASTROPODS  :  Fig.  227,  Stenotbeca  ru- 
gosa ;  228,  Platyceras  primaevum,  x  4 ;  229, 
Hyolithes  Americanus,  x  2 ;  229  a,  operculum 
of  same,  x  2. 


248 


HISTORICAL   GEOLOGY. 


FIG.  230. 


WORM:  burrows  of  Scoli- 
thus  linearis. 


(Orthoceras)  and  forms  with  curved  shells  (Cyrtoceras)-, 

but  not  those  with  spiral  shells,  as  Nautilus. 

Worms.  —  The  existence  of  marine  Worms  among  the 

earliest  animals  of  the  globe  is  proved  by  the  great  num- 
bers of  worm  holes  or  burrows  in  the 
sandstones,  now  filled  with  hard  sand- 
stone like  that  of  the  rock.  They  are 
very  similar  to  the  holes  made  by  such 
worms  in  the  sands  of  seashores  at  the 
present  time.  One  species  has  been 
called  Scolithus  linearis  (Fig.  230). 
These  worm  holes  are  common  in  the 
European  as  well  as  the  American  Cam- 
brian sand-  FIG.  23i. 
stones.  The 
minute  tooth- 
like  bodies 

called    Conodonts,    found    in 

the    Cambrian,  as  well  as  in 

later  formations,  are  probably 

jaws  of  Worms. 

Arthropods.  —  One    of    the 

most  characteristic  groups  of 

the  Cambrian  fauna  was  that 

of    Trilobites,    belonging    to 

the  class  of  Crustaceans.    One 

of  the  largest  of  them,  and  a 

kind  characteristic  of  the  Aca- 
dian, or  Middle  Cambrian,  is 

represented  in  Fig.   231,  one 

third  of  the  natural  size.     Its 

total  length  when  living  must 

have  been  about  ten   inches. 

The    specimen     figured     was 

found  at  Braintree,  south  of 

Boston.       Fig.    232   represents  (natural   size)    a   species 

characteristic  of  the  Georgian,  or  Lower  Cambrian. 


TEILOBITE  :  Paradoxides  Harlani,  x 


CAMBRIAN   EKA. 


249 


shown  in  the  figures,  both  of  these  species  had  large  eyes 
situated  on  the  head  shield. 

Most  specimens  of  Trilobites,  as  illustrated  in  these 
figures,  fail  to  show  antennae,  legs,  or  other  appendages. 


FIG.  232. 


FIG.  283. 


LEPTOSTBACAN  :     Protocaris 
Marshi. 


A  recent  discovery  of  speci- 
mens of  Trilobites  in  the 
Lower  Silurian  showing 
these  parts  (page  258,  Fig. 
253)  has  added  much  to  our 
knowledge  of  the  group. 

Fig.  233  illustrates  an- 
other group  of  Crustaceans 
(the  Leptostracans)  which 
was  (like  the  Trilobites) 
eminently  characteristic  of 
the  Paleozoic. 

Brachiopods  and  Trilo- 
bites among  animals,  and  Seaweeds  among  plants,  make 
up  the  bulk  of  the  living  species  thus  far  discovered. 
There  is  as  yet  no  evidence  that  the  hills  bore  a  Moss  or 
Lycopod,  or  harbored  the  meanest  Insect,  or  that  the 
oceans  contained  a  single  Fish. 


TRILOBITE  :  Olenellus  Vermontanus. 


250  HISTORICAL   GEOLOGY. 

GENERAL  OBSERVATIONS. 

The  ripple-marks,  mud-cracks,  and  tracks  of  animals 
preserved  in  these  most  ancient  of  Paleozoic  rocks  are 
records  left  by  the  waves,  the  sun,  and  the  life  of  the 
period,  as  to  the  extent  and  condition  of  the  continent 
in  that  early  era.  These  markings  teach  that,  when  the 
beds  were  in  progress,  a  large  part  of  the  continent  lay 
at  shallow  depths  in  the  sea,  so  shallow  that  the  little 
currents  made  by  the  waves  could  ripple  its  sands ;  that 
over  other  portions  the  surface  was  a  sand  flat  exposed 
at  low  tide ;  or  a  sea  beach,  the  burrowing  place  of 
worms ;  or  a  mud  flat,  that  could  be  dried  and  cracked 
under  the  heat  of  the  sun,  or  in  a  drying  atmosphere. 

With  such  evidences  of  shallow  water  or  emerged  flats 
in  a  formation  extending  widely  over  the  continent,  it  is 
a  safe  conclusion  that  the  North  American  continent  was 
at  the  time  in  actual  existence,  and  probably  not  far  from 
its  present  extent ;  and,  although  mostly  below  the  sea 
level,  and  in  some  places  somewhat  deeply  so,  it  was 
generally  covered  only  by  shallow  waters,  and  probably 
nowhere  submerged  to  truly  oceanic  depth.  The  same 
was  probably  true  of  the  other  continents.  There  is, 
in  fact,  evidence  of  other  kinds  which,  taken  in  con- 
nection with  the  above,  leaves  little  doubt  that  the  ex- 
isting places  of  the  deep  ocean  and  of  the  continents 
were  determined  even  in  the  first  formation  of  the  earth's 
crust  in  early  Archaean  time,  and  that,  in  all  the  move- 
ments that  have  since  occurred,  the  oceans  and  continents 
have  never  changed  places. 

This  preservation  of  markings,  seemingly  so  perishable, 
on  the  early  shifting  sands,  is  a  very  instructive  fact. 
They  illustrate  part  of  the  means  by  whidh  the  earth  has 
been  recording  its  own  history.  The  track  of  a  Trilobite, 
or  the  furrow  left  by  the  sweep  of  the  wave  over  the 
sand,  is  a  mold,  in  sand  or  earth,  into  which  other 
sands  are  cast  both  to  copy  and  preserve  it;  for,  if  the 


CAMBRIAN   EEA.  251 

waves  or  currents  that  succeed  are  light,  they  simply 
spread  new  sands  over  the  indented  surface,  without 
obliterating  the  mold ;  and  so  the  addition  of  successive 
layers  only  buries  the  markings  more  deeply,  and  thus 
protects  them  against  destruction.  When,  finally,  con- 
solidation takes  place,  the  track  or  ripple-mark  is  made 
as  enduring  as  the  rock  itself. 

The  appearance  in  the  Lower  Cambrian  of  so  many  dif- 
ferent groups  of  pretty  highly  organized  animals,  without 
any  clear  evidence  of  series  of  lower  and  more  embryonic 
forms  preceding  them,  is  one  of  the  most  remarkable  facts 
in  geological  history.  It  has  been  regarded  by  many  as 
affording  a  strong  objection  to  the  theory  of  evolution. 
But  it  must  be  considered  that  the  apparently  abrupt 
introduction  of  the  Cambrian  fauna  may  be  due  to  the 
imperfection  of  the  record.  Both  animal  and  vegetable 
life  was  probably  in  existence  during  the  latter  part  of  the 
Archaean  (page  240),  though  the  general  metamorphism 
of  the  rocks  has  destroyed  or  rendered  unrecognizable 
whatever  fossils  may  have  been  formed.  The  general 
unconformability  between  the  Archaean  and  the  Cambrian 
indicates  an  interval  of  time  whose  record  is  entirely  lost 
(page  57).  As  it  was  a  time  of  great  geographical  change, 
it  may  be  supposed  that  it  was  a  time  in  which  evolution- 
ary changes  in  fauna  and  flora  were  unusually  rapid. 

That  most  of  the  subkingdoms  of  animals  should  appear 
very  early  and  almost  simultaneously,  is  just  what  would 
be  expected  on  evolutionary  grounds.  For  it  is  not  to  be 
supposed  that  the  subkingdoms  were  successively  evolved 
in  an  ascending  series,  but  most  of  them  must  have  been 
independently  evolved  from  ancestral  forms  almost  as 
simple  as  Protozoans.  Moreover,  the  fact  that  almost  all 
groups  of  marine  Invertebrates  have  larval  forms  which 
are  minute,  free  swimming,  and  destitute  of  heavy  skele- 
tons, indicates  that  probably  the  ancestral  forms  from 
which  they  were  derived  were  likewise  minute,  free  swim- 
ming, and  destitute  of  skeletons.  Such  forms  would  be 


252  HISTORICAL  GEOLOGY. 

altogether  unlikely  to  be  preserved  as  fossils.  This  is 
probably  the  principal  reason  for  the  absence  of  any 
record  of  the  ancestors  of  the  Cambrian  fauna. 

II.  LOWER   SILURIAN  ERA. 

SUBDIVISIONS. 

The  name  Silurian  (from  SUures,  the  name  of  an 
ancient  Welsh  tribe)  was  given  by  Murchison,  whose 
studies  in  Wales  and  the  adjacent  parts  of  England  first 
led  to  the  definite  recognition  of  the  Silurian  system. 
The  division  of  the  Silurian  of  Murchison  into  two  eras 
has  been  required  by  later  researches. 

The  Lower  Silurian  era  is  divided  into  two  periods  :  — 
1,  CANADIAN,  and  2,  TRENTON. 

The  Canadian  period  is  so  named  from  Canada,  where 
the  rocks  are  well  displayed  and  have  been  most  thoroughly 
studied;  and  the  Trenton  period,  from  Trenton  Falls,  just 
north  of  U tica,  the  river  at  the  Falls  running  between 
high  bluffs  of  Trenton  Limestone. 

In  Great  Britain  the  first  of  these  periods  is  represented 
by  the  Arenig  group ;  and  the  latter  by  the  Llandeilo 
Flags,  and  the  Bala,  or  Caradoc. 

ROCKS:  KINDS  AND  DISTRIBUTION. 

In  the  Upper  Cambrian,  or  Potsdam,  period,  the  rock 
deposits  formed  over  the  North  American  continent  were 
mainly  of  sand  or  mud,  making  sandstones  aiid  shales ; 
and  but  little  limestone  was  formed.  The  Canadian  period 
is  one  of  transition  to  the  Trenton,  in  which  limestones 
were  in  progress  over  nearly  the  whole  breadth  of  the 
continent,  the  Appalachian  and  Arctic  regions,  as  well  as 
the  Interior  Continental. 

The  rocks  of  the  Canadian  period  along  the  borders  of 
the  Archaean  of  northern  New  York  and  Canada  are:  — 
(1)  A  limestone,  often  arenaceous  and  siliceous,  usually 


LOWER   SILURIAN   ERA.  253 

magnesian,  called  the  Calciferous  Sand  Rock;  (2)  a  purer 
limestone  formation,  mostlj'  magnesian,  called  the  Chazy 
Limestone,  from  a  place  of  that  name  in  northern  New 
York.  In  the  Interior  basin  the  rock  of  the  period  is 
mainly  limestone  —  in  Iowa  and  Wisconsin  the  Lower 
Magnesian  Limestone,  —  excepting  to  the  north,  where 
the  upper  part  is  sandstone  (St.  Peter's  Sandstone). 

The  Trenton  period  opens  with  the  Trenton  epoch, 
which  is  remarkable  for  its  extensive  limestone  formation. 
The  limestone  occurs  in  Canada;  in  New  York  (the  beds 
at  Trenton  Falls  giving  it  its  name);  along  the  Appa- 
lachian range;  in  Ohio  and  other  states  of  the  Ohio  and 
Mississippi  basin;  from  Wisconsin,  northwestward  along 
the  -west  side  of  the  Archaean  area  ;  and  in  the  Arctic 
regions.  It  is  in  most  places  full  of  fossils.  The  Bird's- 
eye  and  Black  River  Limestones  are  part  of  the  Trenton 
formation.  The  rocks  of  the  later  part  of  the  Trenton 
period  (called  the  Utica  and  Hudson  epochs),  in  New 
York  and  the  Appalachians,  are  shale  and  sandstone;  and 
even  in  the  Interior  basin  the  limestones  are  often,  as 
about  Cincinnati,  quite  clayey  or  impure. 

The  crystalline  limestone  (marble)  of  Vermont  and 
western  Massachusetts  and  Connecticut,  with  the  associ- 
ated mica  schist,  hydromica  schist,  clay  slate,  and  quartz- 
ite,  is  partly  Cambrian,  and  partly  Lower  Silurian ;  it 
contains,  at  several  localities,  Canadian  and  Trenton  fos- 
sils. Since  the  rocks  over  most  of  the  region  are  strongly 
metamorphic,  and  consequently  destitute  of  fossils,  the 
limits  of  the  different  formations  cannot  be  precisely 
determined. 

The  thickness  of  the  rocks  of  the  Canadian  and  Tren- 
ton periods  in  Pennsylvania  is  over  7500  feet ;  while  in 
Illinois  it  is  but  750  feet,  and  in  Missouri  about  2000  feet. 

The  rocks  of  this  era  in  Great  Britain  are  chiefly 
shales  and  flags,  with  but  little  limestone.  The  Arenig 
group  at  the  base  of  the  formation  corresponds  approxi- 
mately with  the  Canadian.  The  rocks  of  this  group  are 


254 


HISTORICAL   GEOLOGY. 


FIG.  234. 


overlain  by  the  Llandeilo  Flags.  Above  them  there  are 
the  Caradoc  Sandstone  of  Shropshire,  and  the  Bala  for- 
mation, the  latter  sandy  slates  and  sandstone,  with  thin 
beds  of  limestone,  in  Wales.  In  Scandinavia  the  rocks 
are  mostly  shales,  with  some  limestone,  especially  in  the 
upper  part  of  the  formation. 

LIFE. 

The  life  of  this  era,  like  that  of  the  Cambrian,  was 
chiefly  marine;  but  the  era  is  remarkable  as  showing  the 
first  vestiges  of  terrestrial  life,  both  vegetable  and  animal. 

The  plants  found 
fossil  are  mostly  Sea- 
weeds ;  but  the  Skid- 
daw  Slates  (included 
in  the  Arenig  group) 
of  Great  Britain  have 
afforded  remains  of  a 
plant  (Fig.  234)  which 
has  been  referred  to  the 
Marsileacese,  a  group 
of  the  higher  Crypto- 
gams (Acrogens)  al- 
lied to  the  Ferns  and 
Lycopods. 

All  the  subking- 
doms  of  animals  were 
represented  (except 
the  Tunicates),  the 
earliest  of  Vertebrates 
belonging  to  this  era. 
Moreover,  Arthropods 
were  represented  not 
only  by  the  aquatic  Crustaceans,  but  also  by  the  earliest 
Insects. 

Ccelenterates.  —  The  Lower  Silurian  beds,  especially 
the  finer  shales  and  slates,  are  remarkable  for  the  great 


ACROGEN:   Protannularia  Ilarknessi. 


LOWER   SILURIAN  ERA. 


255 


abundance  of  very  delicate  plumelike  fossils,  called  Grap- 
tolites,  from  the  Greek  ypdcjxo,  to  write. 

A  few  species  from  the  Canadian  are  represented  in 
Figs.  235,  236,  238-240,  and  one  species  from  the  Utica 
epoch  of  the  Trenton  period,  in  Fig.  237.  In  the  living 
state  there  were  cells  along  the  notched  margin,  one  for 
each  notch,  from  which  little  animals  protruded  them- 
selves. They  belong  to  the  Hydroids,  among  the  Hydro- 
zoans.  The  Graptolites  are  especially  characteristic  of 
the  Lower  Silurian,  though  represented  also  in  the  Cam- 
brian and  the  Upper  Silurian. 


FIGS.  235-240. 


GRAPTOLITES  :  Fig.  235,  Loganograptus  Logani,  the  central  portion  of  a  radiating  group  of 
stems,  with  parts  of  the  stems;  236,  same,  portion  of  one  of  the  stems,  enlarged;  236  a, 
part  of  stem,  more  enlarged  ;  237,  Diplograptus  pristis  ;  238,  239,  Phyllograptus  typus ; 
240,  the  young  of  a  Graptolite. 

Fig.  241  represents  one  of  the  Cyathophylloid  Corals 
of  the  Trenton.  Its  shape  is  that  of  a  curved  cone,  a 
little  like  a  short  horn,  the  small  end  being  the  lower. 
At  top,  when  perfect,  the  cavity  of  the  coral  is  divided 
off  by  plates  radiating  from  the  center.  The  name,  Cya- 
thophylloid, from  the  Greek  /eua#o?,  cup,  and  <j>v\\ov,  leaf, 
alludes  to  the  cup  full  of  radiating  leaves  or  plates.  These 
Cyathophylloid  Corals,  which  were  eminently  character- 
istic of  Paleozoic  time,  have  the  radiating  partitions  and 
other  structures  which  are  radially  repeated  in  the  body, 
in  multiples  of  four,  while  in  most  modern  Corals  they 
are  in  multiples  of  six. 

Echinoderms.  —  Fig.  242  shows  the  form  of  one  of  the 


256 


HISTORICAL   GEOLOGY. 


Crinoids,  though  the  stem  on  which  it  stood  is  mostly 
wanting,  and  the  arms  are  not  entire.  There  were  also 
true  Starfishes  in  the  seas. 


FIGS.  241-252. 


ANTHOZOAN:  Fiff.  241,  Streptelasma  corniculnm. — CKTNOTD  :  Fijr.  242,  Taxocrinus  elepans. 
—  HKYO/.OANS:  Fig.  243,  Stictopora  acnta;  244,  Prasopora  lycoperdon  ;  245,  section  of 
same.  —  BRACHIOPODS  :  Fip.  246,  Orthis  testudinaria;  247,  Orthis  occidentalis  :  248, 
Leptaena  sericea.  —  MOLUTSKS:  Fig.  249,  Ambonychia  bellistriata;  250,  Hbapbistoma 
lenticulare ;  251,  Orthoceras  junceuin.  —  TRILUBITE  :  Fig.  252,  Asapbus  platycepha- 
lus,  x  |. 

Molluscoids.  —  Among  Molluscoids,  Bryozoans  were  very 
common.  The  fossils  are  small  cellular  corals :  one  is 
shown  in  Fig.  243. 


LOWER   SILURIAN   ERA.  257 

A  group  of  corals,  mostly  of  small  size,  appearing  in 
hemispherical  (Fig.  244)  or  incrusting  or  branching  forms, 
and  consisting  of  minute  columnar  cells  closely  packed 
together  (Fig.  245),  were  very  abundant  in  the  Lower 
Silurian.  They  were  probably  Bryozoans,  though  re- 
garded by  some  paleontologists  as  true  Anthozoan  corals. 
One  species  is  represented  in  Figs.  244,  245.  Other  im- 
portant genera  of  the  group  are  Monticulipora,  Chcetetes, 
etc. 

Brachiopods  were  still  more  characteristic  of  the  era, 
and  occur  in  vast  numbers.  Three  species  are  repre- 
sented in  Figs.  246-248. 

Mollusks. — All  the  principal  classes  of  Mollusks  were 
represented.  A  Lamellibranch  is  shown  in  Fig.  249,  and 
a  Gastropod  in  Fig.  250.  Shells  of  Cephalopods  were 
especially  common,  under  the  form  of  a  straight  or  curved 
horn  with  transverse  partitions.  Fig.  251  represents  a 
small  species.  One  species  had  a  shell  12  or  15  feet  long, 
and  nearly  a  foot  in  diameter.  The  word  Orthoceras  is 
from  the  Greek  o/?0o?,  straight,  and  fcepas,  horn.  There 
were  some  species  also  of  the  genus  Nautilus,  a  genus 
which  has  survived  to  the  present  time.  While  Trilobites 
appear  to  have  been  the  largest  and  most  powerful  animals 
of  the  Cambrian  seas,  Cephalopods,  of  the  Orthoceras 
family,  far  exceeded  Trilobites  in  both  respects  in  the 
Trenton.  The  larger  kinds  must  have  been  powerful 
animals  to  have  borne  and  wielded  a  shell  12  or  15  feet 
long.  Although  clumsy  compared  with  the  Fishes  of  a 
later  age,  they  emulated  the  largest  of  Fishes  in  size,  and 
no  doubt  also  in  their  voracious  habits. 

Arthropods.  —  Fig.  252  represents  one  of  the  large 
Trilobites  of  the  Trenton  rocks,  the  Asaphus  platycepha- 
lus,  —  a  species  sometimes  found  eight  inches  or  more 
in  length.  Another  genus  of  Trilobites,  very  common  in 
the  Lower  Silurian,  and  represented  also  in  the  Upper 
Silurian,  is  Calymene,  a  species  of  which  is  shown  in 
Fig.  116,  page  77.  The  rocks  of  the  Utica  epoch,  in  a 


258 


HISTORICAL  GEOLOGY. 


locality  near  Rome,  New  York,  have  lately  yielded  a  mul- 
titude of  specimens  of  the  Trilobite  Triarthrus  Beckii,  in 
which  the  legs  and  other  appendages  are  beautifully  pre- 
served. The  species  is  shown,  twice  the  natural  size,  in 
Fig.  253 ;  and  a  more  enlarged  view  of  two  of  the  two- 
branched  legs  is  given  in  Fig.  254. 

An  Insect  allied  to  the  Cockroaches  (Palceoblattina) 
has  been  found  in  Normandy,  in  a  sandstone  probably 
of  the  age  of  the  Caradoc  or  Hudson.  More  recently 


FIG.  253. 


TRILOBITE:  Triarthrus 
Beckii. 


Second  and  third  thoracic  leg  of  Triarthrus 
Beckii,  x  12.  In  II.  the  fringe  of  setae 
has  been  removed,  to  show  more  plainly 
the  joints :  en,  the  main  stem  of  the  leg 
(endopodite)  ;  ex,  the  natatory  branch 
(exopodite). 


has  been  reported  the  discovery  of  an  Insect  in  Sweden 
in  strata  of  about  the  same  age.  These  are  the  earliest 
land  animals  thus  far  discovered. 

Vertebrates.  —  The  earliest  traces  of  Vertebrates  thus 
far  discovered  are  remains  of  Fishes  found  abundantly 
in  a  sandstone  near  Canon  City,  Colorado,  believed  to 
belong  to  the  Trenton  period.  The  remains  are  bony 
plates  of  Placoderms  and  scales  of  Ganoids,  and  struc- 
tures supposed  to  be  the  ossified  sheaths  of  notochords 
(a  rudimentary  form  of  vertebral  column)  of  Selachians. 


LOWER   SILURIAN   ERA.  259 


GENERAL  OBSERVATIONS. 

Geography.  —  The  wide  continental  region  covered  by 
the  Trenton  limestone  formation,  stretching  over  the 
Appalachian  region  on  the  east,  and  widely  through  the 
Interior  basin,  must  have  been  throughout  a  clear  sea, 
densely  populated  over  its  bottom  with  Brachiopods, 
Corals,  Crinoids,  Trilobites,  and  the  other  life  of  the 
era.  It  may,  however,  have  been  a  shallow  sea  ;  for  the 
corals  and  beautiful  shells  of  coral  reefs  live  mostly  within 
100  feet  of  the  surface. 

During  the  later  part  of  the  period,  the  Utica  and 
Hudson  epochs,  the  same  seas,  especially  on  the  north, 
became  more  open  to  sediment,  through  some  change 
of  level  or  of  coast  barriers,  and  consequently  much  of 
the  former  life  disappeared,  and  other  kinds,  adapted  to 
impure  waters  or  to  muddy  bottoms,  supplied  its  place. 

Life.  —  The  appearance  of  the  earliest  land  plants 
(Acrogens),  the  earliest  Insects,  and  the  earliest  Fishes, 
marks  the  progress  in  life  during  the  Lower  Silurian. 

Among  the  genera  of  the  Lower  Silurian,  probably  only 
seven  have  living  species.  These  are  Saccammina  among 
Rhizopocls,  Lingula,  Discina,  Rhynchonella,  and  Crania 
among  Brachiopods,  Avicula  among  Lamellibranchs,  and 
Nautilus  among  Cephalopocls.  Discina  probably  goes  back 
even  to  the  Cambrian,  and  perhaps  Lingula  also,  though  some 
systematists  refer  all  the  supposed  Cambrian  species  to  other 
genera.  These  genera  of  long  lineage  thus  reach  through 
all  time  from  the  Lower  Silurian  onward.  All  other  genera 
disappear — some  at  the  close  of  an  era,  others  at  the  close 
of  a  period,  epoch,  or  other  subdivision  of  an  era. 

The  extinction  of  species  took  place  at  intervals  through 
the  periods,  as  well  as  at  their  close ;  though  the  exter- 
minations at  the  close  of  the  periods  were  more  general. 
With  the  changes  from  one  stratum  to  another,  there  were 
disappearances  of  some  species;  and,  with  the  changes 
from  one  formation  to  another,  still  larger  numbers  of 


260  HISTORICAL  GEOLOGY. 

species  became  extinct.  Scarcely  any  Cambrian  species 
are  known  to  occur  in  the  Canadian  period  ;  very  few 
of  the  species  of  the  Canadian  period  survive  into  the 
Trenton ;  and  very  many  of  those  of  the  early  part  of 
the  Trenton  did  not  exist  in  the  later  part.  Thus  life  and 
death  were  in  progress  together,  species  being  removed, 
and  other  species  appearing,  as  time  moved  on. 

Economic  Products.  —  The  Galena  Limestone  (Trenton 
period)  of  Wisconsin  and  the  adjoining  states  derives  its 
name  from  the  deposits  of  lead  ore  which  it  contains. 
The  ore  occurs  in  cavities  in  the  limestone,  and  its  origin 
was  probably  much  later  than  that  of  the  rock. 

A  large  amount  of  mineral  oil  and  gas  is  afforded  in 
some  regions  by  the  Trenton  formation  and  chiefly  the 
limestone.  At  Findlay,  and  some  other  places  in  Ohio, 
borings  are  made  to  a  depth  of  several  hundred  feet, 
through  the  overlying  rocks,  and  then  for  10  to  50  feet 
into  the  limestone ;  the  gas  comes  up  with  a  rush,  and 
continues  to  escape  for  years.  From  one  boring  over 
a  million  cubic  feet  of  gas  have  been  obtained  per  day. 
The  gas  is  used  both  for  illumination  and  for  fuel.  In 
other  cases  oil  is  obtained,  which,  when  purified,  becomes 
kerosene.  The  gas  consists  chiefly  of  marsh  gas  (CH4), 
the  principal  ingredient  of  ordinary  illuminating  gas ; 
and  the  oil  consists  of  mixtures  of  other  hydrocarbons. 
They  were  produced  by  the  decomposition  of  the  animal 
or  vegetable  substances  in  the  rock,  afforded  by  the  life 
of  the  seas. 

DISTURBANCES  AT  THE   CLOSE   OF  THE  LOWEB, 
SILUftlAK 

Archaean  time  closed,  as  has  been  already  remarked 
(page  240),  with  an  epoch  of  general  upturning  and  meta- 
morphism,  so  that  the  Cambrian  rocks  are  everywhere 
unconformable  with  the  Archaean.  But,  from  that  time 
until  the  close  of  the  Lower  Silurian,  no  extensive  dis- 


TACONIC   REVOLUTION.  261 

turbances  occurred  either  in  eastern  North  America  or  in 
Europe.  The  alternations  of  limestones  with  shales  and 
sandstones  during  the  Eopaleozoic  are  evidence,  indeed, 
that  changes  of  level,  by  gentle  movements  or  oscillations 
of  the  earth's  crust,  were  going  on.  But  the  close  of 
Eopaleozoic  time  was  signalized  by  geographical  changes 
of  a  much  more  striking  character. 

1.  The  Taconic  Range.  —  This  mountain  range,  500 
miles  long,  extending  along  the  western  and  northwestern 
border  of  New  England,  from  Canada  to  northwestern  Con- 
necticut and  Putnam  County  in  eastern  New  York,  was 
made  at  the  close  of  the  Lower  Silurian.  That  the  region 
was  not  dry  land  before,  is  shown  by  the  presence  of 
Chazy  and  Trenton  Limestones,  for  these  are  of  marine 
origin  :  and  that  the  region  was  above  the  water  from  and 
after  this  time,  is  indicated  by  the  fact  that  the  formations 
of  the  Trenton  period  were  the  latest  there  formed ;  and 
by  the  still  more  important  observation  that,  near  Hudson, 
in  the  Hudson  River  valley,  and  at  other  localities,  near 
the  border  of  the  Taconic  region,  there  are  Upper  Silurian 
rocks  overlying  unconformably  the  upturned  older  rocks, 
the  uplift  being  shown  thereby  to  have  preceded  the 
deposit  of  the  Upper  Silurian  rocks. 

During  the  progress  of  the  Lower  Silurian  era  a  great 
thickness  of  rock  had  been  made  over  the  region  of  the 
Taconic  Mountains,  —  probably  15,000  or  20,000  feet. 
These  beds  were  laid  down,  not  in  a  sea  15,000  or  20,000 
feet  deep  until  it  was  full,  but  in  shallow  waters  over  a 
bottom  that  was  gradually  sinking  —  so  gradually  that  the 
rock  material  accumulating  over  it  kept  it  shallow.  Then, 
when  the  slowly  forming  trough  had  reached  this  depth, 
the  epoch  of  catastrophe,  that  is,  of  mountain-making, 
began,  when  the  beds  were  displaced  and  folded,  and 
consolidated  or  crystallized.  Quartzose  sandstones  were 
changed  to  hard  quartzite  —  the  rock  of  high  ridges  in 
Berkshire  and  Vermont ;  earthy  sandstones  were  made 
into  mica  schist  and  gneiss ;  and  common  limestones  came 


262  HISTORICAL   GEOLOGY. 

out  white  or  clouded  marbles,  now  extensively  quarried 
for  architectural  purposes  at  Canaan,  Connecticut,  in 
Berkshire  County,  Massachusetts,  and  at  Rutland  and 
elsewhere  in  Vermont. 

The  history  of  the  Taconic  range  thus  exemplifies  the 
same  stages  already  described  with  reference  to  the  Appa- 
lachian range,  which  has  been  taken  as  a  type  of  mountain 
structure  :  a  slowly  progressing  geosyncline,  in  which  a 
vast  thickness  of  strata  is  accumulated;  the  weakening 
of  the  mass  as  the  bottom  of  the  trough  becomes  heated 
in  its  descent ;  and  finally  the  crushing  of  the  weakened 
strata  to  form  the  complex  folds  characteristic  of  a  syncli- 
norium.  The  Taconic  range  differs,  however,  from  the 
Appalachian  range,  in  that  the  rocks  of  the  former  have 
suffered  a  much  more  intense  degree  of  metamorphism. 

2.  The  Taconic  System. —  It  is  probable,  also,  that  an- 
other mountain  range  was  formed  at  the  same  time,  com- 
mencing in  the  eastern  part  of  Canaan,  Connecticut,  and 
continuing  southward  through  Westchester  County,  New 
York,  to  Manhattan  Island ;    and  still  another,  if  not  a 
continuation  of  the  last,  extending  from  the  vicinity  of 
Philadelphia  to  Buckingham  County,  Virginia  (where  the 
crystalline  rocks  have  afforded  fossils),  and  beyond  this 
southwestward.     These  ranges  extending  southward  and 
southwestward   beyond   the  Taconic   range   proper  have 
suffered  so  much  denudation  as  no  longer  to  constitute 
strongly  marked  geographical  features,  though  the  oro- 
genic  movements  are  indicated  by  the  disturbed  and  meta- 
morphosed rocks.     The  Taconic  revolution,  in  this  view, 
left  its  marks  in  mountains  and  in  crystalline  rocks  along 
the  whole  Atlantic  Border,  and  the  two  or  three  mountain 
ranges  dating  from  that  time  constitute  together  a  long 
Taconic  mountain  system. 

3.  Emergence  of  the  Atlantic  Border  Region.  —  Simul- 
taneously with  the  formation   of  the   Taconic   system,  a 
large  part  of  the  Appalachian  Border  region  was  raised 
above  the  sea  level.     This  is  proved  by  the  fact  that,  along 


UPPER   SILURIAN  ERA.  263 

this  border  south  of  New  York,  no  marine  deposits  are 
known,  of  the  Upper  Silurian  or  of  any  later  formation 
until  the  Cretaceous.  It  is  probable  that  the  geanticlinal 
movement  of  the  Atlantic  Border  region  continued  through 
the  remainder  of  the  Paleozoic,  contemporaneously  with 
the  progress  of  the  Appalachian  geosyncline. 

4.  The  Cincinnati  Uplift.  —  Another  geanticlinal  move- 
ment west  of  the  Appalachian  region  caused  the  emer- 
gence of  two  large  islands  from  the  Interior  Continental 
sea,   one  in  the  region  of   Cincinnati,  the   other  farther 
south  in  Tennessee.     The  axis  of  the  geanticline  trends 
in  general  northeast  and  southwest,  parallel  with  the  trend 
of  the  Appalachians.      This  line  of  shallow  waters  and 
emerged  lands  made  thenceforth  a  partial  division  between 
the  main  body  of  the  Interior  Continental  sea  (Central 
Interior  sea)  and  a  narrow  Eastern  Interior  sea. 

5.  Disturbances  in  Europe.  —  In  the  interior  of  Europe, 
as  in  the  Continental  Interior  region  of  North  America, 
the  Lower  Silurian  rocks  are  generally  overlain  conforma- 
bly by  the  Upper  Silurian.     But  in  Wales  and  western 
England,  where  the  Cambrian  and  Lower  Silurian  rocks 
are  of  great  thickness,  they  are  disturbed  and  metamor- 
phosed, and  separated  from  the  Upper  Silurian  by  well- 
marked  unconformability. 

II.  NEOPALEOZOIC  SECTION. 
I.   UPPER   SILURIAN  ERA. 

The  Eopaleozoic  had  been  characterized  by  the  small 
area  of  dry  land  in  all  the  continents,  and  the  almost  ex- 
clusively marine  flora  and  fauna.  The  Neopaleozoic  was 
characterized  by  a  gradual  increase  in  the  land  areas,  and  a 
progressive  development  of  terrestrial  life,  reaching  a  climax 
in  the  great  forests  of  Acrogens  and  Gymnosperms  which 
characterized  the  Carboniferous  era,  and  the'  varied  terres- 
trial fauna,  including  Snails,  Insects  and  Arachnoids,  Am- 
phibians and  Reptiles,  which  tenanted  the  widening  lands. 


264 


HISTORICAL  GEOLOGY. 


GEOGRAPHICAL  CONDITIONS  AT  THE  OPENING  OF  THE  ERA. 

The  accompanying  map  shows  approximately  the  areas 
where  Archaean  and  Eopaleozoic  rocks  are  surface  rocks, 
and  which  were  therefore  probably,  for  the  most  part, 
dry  land  at  the  beginning  of  the  Upper  Silurian.  There 
may  have  been,  however,  other  areas  which  were  dry 
land  at  that  time,  but  which  have  been  subsequently 

FIG.  255. 


North  America  at  the  opening  of  the  Upper  Silurian. 

covered  by  newer  formations.  The  portion  of  those  areas 
where  Archaean  rocks  are  surface  rocks  is  indicated  by 
a  shading  composed  of  Vs,  except  that,  in  the  Atlantic 
Border  region,  the  Archgean  rocks  have  not  been  fully 
distinguished  from  metamorphic  rocks  of  later  date,  and 
no  attempt  is  therefore  made  to  indicate  their  boundaries 
on  the  map. 

A  comparison  of  this  map  with  that  on  page  237  will 


UPPER   SILURIAN  ERA.  265 

show  that  the  area  of  dry  land  was  not  greatly  increased 
during  the  Eopaleozoic.  The  Atlantic  Border  region, 
south  of  New  York,  had  become  dry  land,  and  was  no 
longer  receiving  deposits.  The  marine  connection  which 
had  existed  between  the  Interior  Continental  sea  and  the 
Atlantic,  through  the  St.  Lawrence  channel,  was  closed 
by  the  elevation  of  land  in  the  region  of  Lake  Champlain. 
It  is,  however,  probable  that  communication  between  the 
Interior  Continental  sea  and  the  Gulf  of  St.  Lawrence 
was  temporarily  reopened  in  the  closing  period  of  the 
Upper  Silurian.  The  Gulf  of  St.  Lawrence  extended 
southward  in  long  bays  in  the  troughs  between  the  eastern 
ridges  of  Archaean  rocks,  and  in  these  bays  Upper  Silurian 
rocks  were  deposited.  The  separation  between  the  Inte- 
rior Continental  sea  and  the  Gulf  of  St.  Lawrence,  and 
the  free  opening  of  the  former  into  the  Pacific,  had  a 
marked  effect  on  the  marine  faunas  of  the  different  regions. 
The  fossils  of  Canada  and  New  England  show  the  influ- 
ence of  migration  from  western  Europe ;  while  the  Interior 
Continental  sea  was  open  to  immigration  from  the  old 
world  chiefly  by  way  of  the  Pacific.  An  Eastern  Interior 
sea  or  bay  was  imperfectly  separated  from  the  main  body 
of  the  Interior  Continental  sea  by  the  line  of  islands  and 
shallows  formed  by  the  Cincinnati  uplift ;  and  it  was  in 
the  eastern  part  of  this  bay  that  the  vast  subsidence  of 
the  Appalachian  geosyncline  was  in  progress. 

SUBDIVISIONS. 

The  Upper  Silurian  era  in  North  America  includes  three 
periods:  —  1,  NIAGARA;  2,  ONONDAGA;  3,  LOWER  HEL- 

DERBERG. 

The  name  of  the  first  is  from  the  Niagara  River,  along 
which  the  rocks  are  displayed  ;  that  of  the  second,  from 
the  name  of  a  town  and  county  in  central  New  York ; 
that  of  the  third,  from  the  Helderberg  Mountains,  south 
of  Albany,  where  the  lower  rocks  are  of  this  period. 


266  HISTORICAL   GEOLOGY. 


ROCKS:    KINDS  AND  DISTRIBUTION. 

1.  Niagara  Period.  — The  rocks  of  the  Niagara  period, 
in  the  eastern  part  of  the  Interior  Continental  region  oi 
North  America,  are  :  —  (1)  A  conglomerate  and  grit  rock 
called   the    Oneida   Conglomerate,   which    extends   from 
central    New   York    southward    along    the    Appalachian 
region,  having   a   thickness   of   700  feet   in   some   parts 
of    Pennsylvania ;     which,    together    with    the    Medina 
Sandstone,  spreading  westward  from  central  New  York 
through   Michigan,   and   also   southward  along   the  Ap- 
palachian region,  being  1500  feet  thick  in  Pennsylvania, 
is  included  in  the  Medina  epoch ;   (2)  Hard  sandstones, 
or  flags  and   shales,  with  some  limestones  (particularly 
westward)    and   some    beds    of    iron    ore,   belonging    to 
the   Clinton  epoch,  having  nearly  the  same  distribution 
as   the  Medina  formation,  though  a  little  more  widely 
spread  in  the  west,  and  about  2000  feet  thick  in  Pennsyl- 
vania ;   (3)  The  formations  of  the  Niagara  epoch,  occur- 
ring in  New  York  from  the  Hudson  to  the  Niagara,  and 
extending  widely  over  the  Interior  Continental  region; 
they  consist,  at  Niagara,  of  shale  below  and  thick  lime- 
stone above,  but  mainly  of  limestone  in  the  Interior  region. 
The  Niagara  is  one  of  the  great  limestone  formations  of 
the  continent,  existing  also  in  the  Arctic  regions. 

Ripple-marks  and  mud-cracks  are  very  common  in  the 
Medina  formation.  The  example  of  rill-marks  figured  on 
page  155  is  from  its  strata  in  western  New  York. 

The  section,  Fig.  256,  represents  the  rocks  on  the  Niagara 
River  at  and  below  the  Falls.  The  Falls  are  at  F ;  the 
Whirlpool,  three  miles  below,  at  W;  and  the  Lewiston 
Heights,  which  front  Lake  Ontario,  at  L.  Nos.  1,  2,  3,  4 
are  different  sandstone  and  shale  strata  of  the  Medina 
epoch ;  5,  shale,  and  6,  limestone,  of  the  Clinton  epoch ; 
7,  shale,  and  8,  limestone,  of  the  Niagara  epoch. 

2.  Onondaga   Period.  —  The    rocks    of    the    Onondaga 
period  include  the  Salina  beds  and  the  Water-lime  group. 


UPPER   SILURIAN   ERA.  267 

The  Salina  beds  are  fragile,  clayey  sandstones  and  shales, 
usually  reddish  in  color,  and  including  a  little  limestone. 
They  occur  in  New  York,  in  western  Ontario,  and  in  the 
vicinity  of  Cleveland,  Ohio. 

The  salt  of  Salina  and  Syracuse,  in  central  New  York, 
is  obtained  from  wells  of  salt  water  150  feet  and  upward 
in  depth,  which  are  borings  into  these  saliferous  rocks. 
From  35  to  45  gallons  of  the  water  afford  a  bushel  of  salt, 
while  of  sea  water  it  takes  350  gallons  for  the  same  amount. 
No  solid  salt  is  there  found ;  but  farther  south  and  west 
one  or  more  beds  of  rock  salt  occur  over  an  area  measur- 
ing 150  miles  from  east  to  west  and  probably  not  less 
than  60  miles  from  north  to  south.  The  aggregate  thick- 
ness of  these  salt  beds  varies  widely,  being,  in  the  vicinity 
of  Ithaca,  about  250  feet,  though  much  less  than  that  in 
most  places.  At  Ithaca,  the  total  thickness  of  the  Salina 
formation  is  1230  feet,  and  it  is  covered  by  1900  feet  of 
later  strata.  Beds  of  rock  salt  are  also  found  at  Gode- 
rich,  Ontario,  and  near  Cleveland. 

The  rocks  of  the  Water-lime  group  are  impure  mag- 
nesian  limestones.  Owing  to  these  impurities,  the  quick- 
lime made  from  the  rock  will  set  under  water,  and  is 
accordingly  used  in  the  manufacture  of  hydraulic  cement. 
The  name  of  the  group  refers  to  that  fact. 

Both  the  Salina  and  the  Water-lime  beds  contain  gypsum, 
sometimes  in  layers,  sometimes  in  imbedded  masses.  In 
some  cases  it  may  have  been  formed  directly,  like  the  salt, 
by  the  evaporation  of  sea  water.  But  much  of  it  has 
resulted  from  the  decomposition  of  the  limestone  by  the 
action  of  sulphuric  acid  derived  from  the  oxidation  of  the 
sulphuretted  hydrogen  dissolved  in  subterranean  waters. 
Sulphur  springs  are  common  in  the  region. 

3.  Lower  Helderberg  Period.  —  The  Lower  Helderberg 
group  consists  mainly  of  limestones,  and  is  the  second 
limestone  formation  of  the  Upper  Silurian.  The  forma- 
tion is  well  developed  in  the  State  of  New  York  and 
along  the  Appalachian  region  to  the  south.  It  also 


268  HISTORICAL   GEOLOGY. 

occurs  in  Tennessee  and  probably  in  southern  Illinois; 
but  the  beds  are  thin  or  wanting  over  most  of  the  Central 
Interior  region.  The  formation  is  also  found  in  Canada 
in  the  line  of  the  Connecticut  Valley,  in  northern  Maine, 
and  in  New  Brunswick  and  Nova  Scotia. 

Upper  Silurian  Rocks  in  Europe.  —  In  Great  Britain 
the  base  of  the  Upper  Silurian  rocks  is  formed  by  con- 
glomerates, sandstones,  and  shales,  called,  where  occurring 
in  South  Wales,  the  Llandovery  group,  and  corresponding 

FIG.  256. 


L  W 

Section  along  the  Niagara,  from  the  Falls  to  Lewiston  Heights. 

to  the  Medina  and  Clinton  groups.  Above  these  there  is 
the  Wenlock  group,  consisting  of  limestone  and  some 
shale  (including,  in  the  upper  portion,  the  Dudley  Lime- 
stone), and  corresponding  to  the  Niagara  group.  These 
rocks  occur  as  surface  rocks  near  the  borders  of  Wales 
and  England.  Next  comes  the  Ludlow  group,  of  the  age 
of  the  Onondaga  and  Lower  Helderberg  beds. 

LIFE. 

The  limestone  strata  and  most  of  the  other  beds  of  the 
Niagara  group  are  full  of  fossils;  and  so  also  are  the  rocks 
of  the  Lower  Helderberg  period,  and  of  the  Wenlock  and 
Ludlow  formations  in  Great  Britain.  Fossils  are  well-nigh 
wanting  in  the  Salina  beds,  and  not  abundant  in  the  Water- 
lime. 

The  life  of  the  era  was  the  same  in  general  features  as 
that  of  the  latter  part  of  the  Lower  Silurian,  though  mostly 
different  in  species. 

The  most  of  the  vegetable  remains  are  those  of  Sea- 
weeds ;  but  the  Lower  Helderberg  rocks  of  this  country 


UPPER    SILURIAN    ERA. 

FIGS.  257-269. 


269 


257 


ANTHOZOANS  :  Fig.  257,  Zaphrentis  bilateralis,  Clinton  group ;  258,  Favosites  Niagarensis, 
Niagara  group;  259,  Halysites  catenulatus,  ibid.  —  CYSTOID  :  Fig.  260,  Caryocrinus 
ornatus,  Niagara  group.  —  BRACIIIOPODS  :  Fig.  261,  Pentamerus  oblongus,  Clinton  and 
Niagara  groups,  also  Llandovery  and  Wenlock ;  262,  Orthis  varica,  x  2,  Niagara  group 
and  Dudley  Limestone ;  263,  Lepta-na  transversalis,  ibid.  ;  264,  Strophomena  rhom- 
boidalis,  ibid.  ;  265,  Rhynchotreta  cuneata,  ibid. — LAMELMBRANCH  :  Fig.  266,  Avicula 
emacerata.  Niagara  group.  —  GASTROPODS  :  Fig.  267,  Cyclonema  cancellatum,  Clinton 
group  ;  '268,  Platyceras  angulatum,  Niagara  group.  —  TRILOBITB  :  Fig.  269,  Homalonotus 
delphinocephalus,  x  J,  Niagara  group. 


270  HISTORICAL  GEOLOGY. 

have  afforded  a  few  remains  of  Acrogens,  representing 
apparently  both  the  Equiseta  and  the  Lycopods. 

Among  animals,  the  Coelenterates  were  represented 
chiefly  by  Anthozoan  corals,  the  Echinoderms  by  Crinoids, 
and  the  Molluscoids  by  Brachiopods.  The  last  are  espe- 
cially abundant,  their  shells  outnumbering  all  other  fossils. 
All  the  principal  classes  of  Mollusks  were  represented, 
Cephalopods  of  the  Orthoceras  group  being  most  charac- 
teristic. Arthropods  were  represented  by  Trilobites,  Os- 
tracoids,  and  Leptostracans,  among  Crustaceans,  also  by 
Merostomes,  Arachnoids,  and  Insects.  The  only  Verte- 
brates were  Fishes. 

Coelenterates.  —  Fig.  257  is  a  coral  of  the  Cyathophyl- 
loid  group,  showing  the  radiating  plates  of  the  interior ; 
Fig.  258,  a  species  of  Favosites,  a  genus  in  which  the  cells 
have  a  columnar  form  (somewhat  honeycomb-like,  whence 
the  name,  from  Latin  favus,  honeycomb),  and  are  divided 
by  transverse  partitions;  Fig.  259,  a  Chain  Coral,  Haly sites 
(Greek  aXim?,  chain),  the  cells  appearing,  in  a  transverse 
section,  like  links  of  a  chain. 

Echinoderms.  —  Fig.  260  is  a  Cystoid  with  the  arms 
broken  off.  Another  Cystoid  of  the  Niagara  group  is 
shown  in  Fig.  82,  on  page  67.  A  Starfish,  also  of  the 
Niagara,  is  shown  in  Fig.  86,  on  page  68. 

Molluscoids.  —  Figs.  261-265  are  Brachiopods  of  the 
Niagara  period  ;  Figs.  270-274,  Brachiopods  of  the  Lower 
Helderberg. 

Mollusks.  —  Fig.  266  is  a  Lamellibranch,  and  Figs. 
267,  268,  Gastropods,  of  the  Niagara  period. 

Fig.  275  represents  small,  slender,  tubular  cones,  called 
Tentaculites,  which  almost  make  up  the  mass  of  some  layers 
in  the  Water-lime  group  ;  the  form  of  one  enlarged  is  shown 
in  Fig.  276 ;  they  are  regarded  as  shells  of  Pteropods. 
The  same  genus  is  abundant  also  in  the  Lower  Helderberg. 

Arthropods.  —  Fig.  269  is  a  reduced  figure  of  a  common 
Trilobite  of  the  Niagara  group.  The  species  is  often  8 
or  10  inches  in  length. 


UPPER   SILURIAN   ERA. 


271 


Fig.  277  is  an  Ostracoid  Crustacean,  Leperditia  alta, 
of  unusually  large  size  for  that  group,  modern  Ostracoids 
seldom  exceeding  a  twelfth  of  an  inch  in  length. 

Fig.  278  is  a  Eurypterus,  a  representative  of  the  class 
of  Merostomes,  of  which  the  Limulus,  or  Horseshoe  Crab, 
is  now  the  sole  surviving  genus.  The  Eurypterus  group 
makes  its  first  appearance  in  the  Utica  Shale,  but  is  more 
characteristic  of  Neopaleozoic  time,  attaining  its  greatest 


FIGS.  270-278. 


270 


271 


BEACHIOPODS  :  Figs.  270,  271,  Pentamerus  galeatus ;  272,  273,  Ehynchonella  ventricosa ; 
274,  Spirifer  macropleurus.  —  PTEROPOD  :  Fig.  275,  Tentaculites  gyracanthus ;  276, 
same,  enlarged.  —  OSTRACOID  :  Fig.  277,  Leperditia  alta.  —  MEROSTOME  :  Fig.  278,  Euryp- 
terus reinipes,  a  small  specimen.  Figs.  270-274  are  species  from  the  Lower  Helderberg ; 
Figs.  275-278,  from  the  Water-lime. 

development  in  the  Upper  Silurian.  The  species  figured 
is  from  the  Water-lime,  and  is  sometimes  nearly  a  foot  long. 
Species  of  the  same  order  occur  in  Great  Britain  in  the 
Wenlock  and  Ludlow  beds,  and  one  of  them  is  supposed, 
from  the  fragments  found,  to  have  been  6  or  8  feet  long, 
far  surpassing  any  Arthropod  now  living.  The  Upper 
Silurian  of  Great  Britain  has  also  afforded  forms  still 
more  closely  related  to  the  modern  Limulus, 


272  HISTORICAL   GEOLOGY. 

Arachnoids  are  represented  by  Scorpions,  which  have 
been  found  in  the  Water-lime  group  in  New  York,  and 
also  in  the  Upper  Silurian  of  Scotland  and  Sweden. 

Vertebrates.  —  Remains  of  Fishes  have  been  found  in 
the  Clinton  and  the  Water-lime  of  this  country,  and  in 
the  Ludlow  beds  of  Great  Britain.  They  include  plates 
of  Placoderms,  and  probably  fin  spines  of  Selachians. 

GENERAL  OBSERVATIONS. 

On  the  map,  page  235,  the  areas  over  which  the  Cam- 
brian and  Silurian  formations  are  surface  rocks  are  distin- 
guished by  being  horizontally  lined.  It  is  observed  that 
they  spread  southward  from  the  northern  Archaean  area, 
and  indicate  an  extension  of  the  growing  continent  in  that 
direction.  . 

South  of  the  Silurian  area  commences  the  Devonian, 
which  is  vertically  lined;  and  the  limit  between  them  shows 
approximately  the  course  of  the  seashore  at  the  close  of 
the  Upper  Silurian  era.  It  is  seen  that  more  than  half  of 
New  York,  and  nearly  all  of  Canada  and  Wisconsin,  had 
by  that  time  become  part  of  the  dry  land ;  but  a  broad 
bay  covered  the  Michigan  region  to  the  northern  point  of 
Lake  Michigan,  for  here  Devonian  rocks,  and  to  some 
extent  Carboniferous,  were  afterward  formed.  The  Ar- 
chaean dry  land,  the  nucleus  of  the  continent,  had  also 
received  additions  in  a  similar  manner  on  its  eastern  and 
western  sides,  through  British  America.  And  there  may 
have  been  other  areas  of  dry  land  which  were  subse- 
quently submerged  and  covered  by  more  recent  strata. 

But,  with  all  the  increase,  the  amount  of  dry  land  in 
North  America  was  still  small.  Europe  is  proved  by 
similar  evidence  to  have  had  much  submerged  land.  The 
surface  of  the  earth  was  a  surface  of  great  waters,  with 
the  continents  only  in  embryo  —  one  large  area  and  some 
islands  representing  that  of  North  America,  and  an  archi- 
pelago that  of  Europe.  The  emerged  land,  moreover, 
was  most  extensive  in  the  higher  latitudes.  The  rivers 


UPPER   SILURIAN    ERA.  273 

of  a  world  whose  lands  were  so  small  must  also  have  been 
small.  The  lands,  too,  according  to  present  evidence,  had 
no  greensward  over  the  rocks,  until  the  latter  part  of  the 
Silurian  age. 

The  succession  of  Upper  Silurian  formations  is  as 
follows  :  —  (1)  The  Medina  Sandstone,  having  at  its  base 
the  coarse  grit  called  Oneida  Conglomerate,  occurring  in 
great  thickness  along  the  Appalachian  region,  and  reach- 
ing north  to  central  New  York,  and  spreading  west- 
ward beyond  the  limits  of  that  state  ;  (2)  The  Clinton 
group  of  flags  and  shales,  with  some  limestone  (especially 
westward),  having  the  same  Appalachian  extension  and 
great  thickness,  but  spreading  on  the  north  much  farther 
westward,  even  to  the  Mississippi;  (3)  The  Niagara  group, 
represented  in  New  York  by  shales  and  limestones,  and 
spreading  as  a  great  limestone  formation  through  the 
larger  part  of  the  Interior  region ;  (4)  The  Salina  salt- 
bearing  shales  of  New  York,  extending  west  through 
Canada,  and  over  part  of  the  Appalachian  region  south- 
west ;  (5)  Another  limestone,  but  mostly  impure,  spread- 
ing over  New  York  State  and  the  Appalachian  region, 
and  also  some  of  the  states  west,  and  occurring  in  the 
northward  extension  of  the  Connecticut  Valley,  and  over 
Maine  to  the  Gulf  of  St.  Lawrence. 

These  facts  teach  that  geographical  changes  took  place 
from  time  to  time,  in  the  course  of  the  era,  corresponding 
to  these  several  changes  in  the  formations.  The  clear  con- 
tinental seas  of  the  Trenton  period  were  succeeded  by 
conditions  fitted  to  produce  the  several  arenaceous  and 
argillaceous  formations,  of  varying  limits,  which  followed ; 
but  clear  waters  returned  again  at  the  epoch  of  the 
Niagara  group,  when  corals,  crinoids,  and  shells  covered 
the  bottom  of  the  continental  sea,  and  made  the  Niagara 
limestone  formation.  But  these  seas  in  the  Niagara 
epoch  were  less  extended  than  those  of  the  Trenton,  not 
covering  the  Appalachian  region.  The  Niagara  epoch 
of  limestone-making  was  followed  by  the  Onondaga  or 


274  HISTORICAL   GEOLOGY. 

Saliferous  period.  Since  the  beds  (1)  are  clays  and 
clayey  sands,  (2)  are  almost  wholly  without  fossils,  and 
(3)  afford  salt,  it  may  be  inferred  that  central  New  York 
was  at  the  time  a  great  salt  marsh,  mostly  shut  off  from 
the  sea.  Over  such  an  area  the  waters  would  at  times 
become  too  salt  to  support  life,  owing  to  partial  evapora- 
tion under  the  hot  sun,  and,  possibly,  too  fresh  at  other 
times  from  the  rains.  Moreover,  muddy  deposits  would 
be  formed ;  for  such  deposits  are  now  commonly  formed 
in  salt  marshes.  The  salt  water  would  deposit  salt  by 
evaporation  in  dry  seasons,  and  from  time  to  time,  by  an 
occasional  ingress  of  the  sea,  salt  water  would  be  resup- 
plied  for  further  evaporation. 

There  is  direct  testimony  as  to  the  condition  of  the  land 
and  shallowness  of  the  waters  in  the  regions  where  many 
of  the  rocks  were  in  progress  ;  for  ripple-marks  and  mud- 
cracks  are  common  in  some  layers,  and  are  positive  evi- 
dence that  the  sands  and  earth  that  are  now  the  solid 
rock  were  then  the  loose  sands  of  beaches,  sand  flats,  or 
sea  bottoms,  or  the  mud  of  a  salt  marsh.  Such  little 
markings,  therefore,  remove  all  doubt  as  to  the  condition 
of  central  New  York  during  the  deposition  of  the  Salina 
beds. 

Similar  markings  indicate,  also,  the  precise  condition  of 
the  region  of  the  Medina  Sandstone,  showing  that  there 
were  sand  flats,  sea  beaches,  and  muddy  bottoms  open 
to  the  inflowing  sea.  Where  the  rill-marks  were  made 
(Fig.  186,  page  155),  the  sands  were  those  of  a  gently 
sloping  flat  or  beach  ;  the  waters  swept  lightly  over  the 
sands,  dropping  here  and  there  a  stray  shell  (as  the  Lingula 
cuneata  shown  in  the  figure)  or  a  pebble,  which  became 
partly  buried  ;  and  then,  as  they  retreated,  they  made  a 
tiny  .plunge  over  the  little  obstacle,  and  furrowed  out  the 
loose  sand  below  it.  The  fineness  of  the  sand,  lightness 
of  the  shells,  and  small-ness  of  the  furrows  are  proof  that 
the  movements  were  light. 

The  great  thickness  of  most  of  the  formations  of  the 


DEVONIAN    ERA.  275 

Upper  Silurian  along  the  Appalachian  region  leads  to 
many  interesting  conclusions.  The  Appalachian  region 
was  in  strong  contrast  with  the  Central  Interior  region, 
where  the  series  of  contemporaneous  beds  is  hardly  one 
tenth  as  thick.  Taking  this  into  connection  with  another 
fact,  that  very  many  of  the  strata  among  the  thousands  of 
feet  of  Upper  Silurian  formations  in  the  Appalachian  re- 
gion contain  those  evidences  of  shallow-water  and  mud-flat 
or  sand-flat  origin  above  explained,  there  is  full  proof  that, 
in  the  Upper  Silurian  era,  the  region  was  for  the  most  part 
a  shallow  sea  border  receiving  the  debris  from  the  Atlantic 
Border  region,  which  had  emerged  as  a  land  area  at  the 
close  of  the  Lower  Silurian.  The  great  thickness  of  the 
strata  was  rendered  possible  by  the  progressive  subsi- 
dence which  was  preparing  the  Appalachian  region 
for  the  mountain-making  epoch  at  the  close  of  Paleo- 
zoic time. 

During  the  Cambrian  and  Lower  Silurian  eras  a  similar 
gradual  subsidence  had  permitted  the  accumulation  of  the 
thick  series  of  strata  which  were  upturned  and  metamor- 
phosed in  the  making  of  the  Taconic  Mountains.  The 
subsiding  area  during  the  Upper  Silurian  era  extended 
from  Pennsylvania  northward  into  New  York,  and  not 
along  the  Taconic  region;  the  rocks  in  the  state  of  New 
York  have  great  thickness  for  some  distance  beyond  the 
Pennsylvania  border. 

II.   DEVONIAN   ERA. 

SUBDIVISIONS. 

The  Devonian  formation  was  so  named  by  Sedgwick 

and  Murchison,  from  Devonshire,  England,  where  it  occurs. 

The  era  may  be  divided  into  four  periods :  —  1,  OBIS- 

KANY  ;    2,    CORNIFEROUS  ;    3,    HAMILTON  ;    4,    CHEMUNG. 

The  Oriskany  and  Corniferous  periods  are  often  called 
Lower  Devonian;  the  Hamilton,  Middle  Devonian;  and 
the  Chemung,  Upper  Devonian. 


276 


HISTORICAL   GEOLOGY. 


ROCKS:  KINDS  AND  DISTRIBUTION. 

1.  Oriskany  Period.  —  The   Oriskany  beds   are  mostly 
rough  calcareous  sandstones.     The  formation  extends  from 
Oriskany,  New  York,  southward  along  the  Appalachian 
region  through   Pennsylvania,  Maryland,  and   Virginia, 
where  it  is  several  hundred  feet  thick.     It  occurs  also  in 
northern  Maine,  and  at  Gaspe  on  the  Gulf  of  St.  Lawrence, 
where  the  rock  is  partly  limestone. 

2.  Corniferous  Period.  —  The  lowest  rocks  of  this  period 
are  fragmental  beds,  called  the  Cauda-Cralli  Grit  and  the 
Schoharie  Grrit,  having  their  distribution  along  the  Appa- 
lachian region,  commencing  in  central  and  eastern  New 
York,  and  extending  southwestward  into  Pennsylvania. 

Next  follows  the  great  Corniferous  Limestone,  the  lower 
part  of  which  is  sometimes  called  the  Onondaga  Limestone, 
and  the  whole  of  which  is  often  called  the  Upper  Helder- 
berg  group.  It  stretches  from  eastern  New  York  westward 
to  the  states  beyond  the  Mississippi. 

The  name  Corniferous  (derived  from  the  Latin  cornu, 
horn)  was  given  it  by  Eaton,  from  its  frequently  contain- 
ing a  variety  of  quartz  called  hornstone.  This  hornstone 
differs  from  true  flint  in  being  less  tough,  or  more  splin- 
tery in  fracture,  though  it  is  like  it  in  hardness  and  in 
consisting  of  silica. 

The  limestone  is  in  many  places  literally  an  ancient 
coral  reef.  It  contains  corals  in  vast  numbers  and  of 
great  variety;  and  in  some  places,  as  at  the  Falls  of  the 
Ohio,  near  Louisville,  Kentucky,  the  resemblance  to  a 
modern  reef  is  perfect.  Some  of  the  coral  masses  at  that 
place  are  5  or  6  feet  in  diameter;  and  single  polyps  of 
the  Cyathophylloid  corals  had  in  some  species  a  diameter 
of  2  or  3  inches,  and  in  one  species  a  diameter  of  6  or  7 
inches. 

The  same  reef  rock  occurs  near  Lake  Memphremagog 
on  the  borders  of  Vermont  and  Canada,  and  also  at  Little- 


DEVONIAN   ERA.  277 

ton,  New  Hampshire ;  but  the  corals  have  in  these  places 
been  partly  obliterated  by  metamorphism. 

The  Corniferous  Limestone  in  some  places  abounds  in 
mineral  oil.  The  oil  wells  of  Enniskillen,  Ontario,  are 
from  this  rock. 

3.  Hamilton  Period. — The  Hamilton  formation  consists 
in  New  York  of  sandstones  and  shales,  with  a  few  thin 
layers  of  limestone.     It  consists  of  two  parts  correspond- 
ing to  two  epochs  :  the  lower  part  is  called  the  Marcellus 
Shale;  the  upper,  the  Hamilton  beds.     It  has  its  greatest 
thickness  along  the  Appalachians.      From  New  York  it 
spreads  westward,  where  it  is  in  part  calcareous.      The 
formation  occurs  also  in  New  Brunswick,  and  at  Gaspe, 
on  the  Gulf  of  St.  Lawrence. 

The  Hamilton  beds  afford  an  excellent  flagging  stone 
in  central  New  York,  and  on  the  Hudson  River,  near 
Kingston,  Saugerties,  Coxsackie,  and  elsewhere,  which  is 
extensively  quarried  and  exported  to  other  states. 

4.  Chemung   Period.  —  The    Chemung   period   includes 
two  epochs,  the  Portage,  and  the   Chemung  proper.     The 
Portage  beds  are  mainly  shales  and  shaly  sandstones ;  the 
Chemung   beds   mainly  sandstones,  or   shaly  sandstones, 
with  some  conglomerate.      The  base  of   the   Portage   is 
formed  by  a  stratum  of  black  bituminous  shale  called  the 
Genesee  Shale.     The  beds  of  the  Chemung  period  spread 
over  a  large  part  of  southern  and  western  New   York, 
attaining  a  thickness  of  between  2000  and  3000  feet. 

In  the  following  section,  taken  on  a  iiorth-and-south 
line  south  of  Lake  Ontario,  No.  6  represents  the  beds  of  the 
Onondaga  period ;  7,  the  Lower  Helderberg  Limestone ; 
9,  the  Corniferous,  or  Upper  Helderberg,  Limestone  ;  10  a, 
6,  the  Hamilton  beds  ;  11  a,  the  Genesee  Shale  ;  and  11  6, 
the  overlying  beds  of  the  Chemung  group. 

In  the  Catskill  Mountains,  the  Portage  and  Chemung 
epochs  are  not  distinguished  from  each  other,  being  jointly 
represented  by  a  mass  of  sandstones,  varying  into  con- 
glomerates and  shales,  predominantly  red,  called  the  Cats- 


278 


HISTORICAL   GEOLOGY. 


kill  group.  The  rocks  in  the  Catskills  have  a  thickness  of 
3000  feet.  The  same  formation  extends  southwestward 
along  the  Appalachians  into  Pennsylvania,  attaining  near 
Mauch  Chunk  a  thickness  of  more  than  7500  feet. 

The  Upper  Devonian,  like  most  of  the  Paleozoic  forma- 
tions, is  much  thinner  in  the  Central  Interior  region  than 
along  the  Appalachians.  It  is  chiefly  represented  in 
the  Central  Interior  by  a  bituminous  shale  resembling  the 

FIG.  279. 


6  7  y 

Section  of  Upper  Silurian  and  Devonian  formations  south  of  Lake  Ontario. 

Genesee  Shale  of  New  York,  and  commonly  called  the 
"Black  Shale."  In  Ohio,  the  Upper  Devonian  is  repre- 
sented by  the  Huron,  Erie,  and  Cleveland  Shales. 

The  Upper  Devonian  is  the  great  "  oil  horizon "  of 
Pennsylvania. 

Devonian  Rocks  in  Europe.  —  In  Great  Britain  the 
Devonian  rocks  include  the  Old  Red  Sandstone,  the 
prevailing  rock  of  the  age  in  Wales  and  Scotland;  and 
slates  and  limestones  in  Devon  and  Cornwall.  The  thick- 
ness of  the  Old  Red  Sandstone  in  some  places  in  Scotland 
is  said  to  be  10,000  to  16,000  feet.  The  Devon  beds  are 
estimated  to  be  10,000  to  12,000  feet  in  thickness.  The 
distribution  in  Great  Britain  is  shown  on  the  map,  page 
295.  In  Germany,  in  the  Rhenish  provinces,  there  is  a 
coral  limestone  very  similar  to  that  of  North  America. 


LIFE. 
GENERAL  CHARACTERISTICS. 


The  Devonian  was  characterized  by  forests  and  an 
abundance  of  Insects  over  the  land,  and  by  Fishes  of 
many  kinds  in  the  waters.  The  earliest  Amphibians 
probably  appeared  in  this  era. 


DEVONIAN   ERA. 


279 


PLANTS. 

Cryptogams.  —  The  hornstone  of  the  Cornif erous  and 
other  limestones  develops,  under  the  microscope,  the  fact 
that  it  was  probably  made  from  the  siliceous  remains  of 
plants  and  animals,  —  shells  of  Diatoms,  spicules  of 
Sponges,  and  other  organic  relics  having  been  detected 
in  it. 

Figs.  280-282  represent  portions  of  some  of  the  land 
plants.  Fig.  282  is  a  fragment  of  a  Fern,  and  Figs.  280, 


FIGS 


I 


ACROGKNS  :  Fig.  280,  Lepidodendron  primaevum,  from  the  Hamilton  group ;  281,  Sigillaria 
Hallii,  ibid. ;  282,  Archseopteris  Halliana,  from  the  Chemung  group. 

281,  are  portions  of  Lycopodiaceous  trees.  The  scars  or 
prominences  over  the  surface  are  the  points  of  attachment 
of  the  fallen  leaves;  a  dried  branch  of  a  Norway  Spruce, 
stripped  of  its  leaves,  looks  somewhat  like  Fig.  281.  By 
referring  to  page  88,  it  will  there  be  seen  that  among 
the  Flowerless  Plants  or  Cryptogams  there  is  one  group, 
the  highest,  that  of  Acrogens,  in  which  the  plants  have 
upward  growth  like  ordinary  trees,  and  the  tissues  are 
partly  vascular:  it  is  the  one  containing  the  Ferns,  Lyco- 
pods,  and  Equiseta  or  Horsetails.  The  most  of  the  land 


280  HISTORICAL   GEOLOGY. 

plants  of  the  Devonian  belong  to  the  three  orders  just 
mentioned. 

A  somewhat  fuller  description  of  these  groups  is  here 
appropriate,  since  in  the  Devonian  era,  for  the  first  time, 
they  attained  such  development  as  to  clothe  the  land  with 
forests. 

1.  Ferns. — The  species  have  a  general  resemblance  to 
the  Ferns  or  Brakes  of  the  present  time. 

2.  Lycopods.  —  These  are  plants  related  to  the  Ground 
Pine.     The  existing  plants  of  this  tribe  are  slender  species, 
seldom  more  than  a  few  inches  in  height,  though  the  creep- 
ing stems  of  some  species  may  be  many  feet  in  length. 
Some  of   the  ancient  species  were  of  the  size  of  forest 
trees.     These  ancient  species  belong  mostly  to  two  groups, 
of  which  the  genera  Lepidodendron  and  Sigillaria,  respec- 
tively, are  the  types.     In  the  former,  the  scars  are  con- 
tiguous,  and   are   arranged  in  quincunx  order,  that   is, 
alternate  in  adjoining  rows,  as  shown  in  Fig.  280.     The 
name  Lepidodendron  is  from  the  Greek  XeTrt?,  scale,  and 
§ev$pov,  tree,  and  alludes  to  the  scar-covered  trunk,  which 
looks  somewhat  like  a  scale-covered  reptile.     The  Sigil- 
larids  include  trees  of  moderate  height,  with  stout,  spar- 
ingly branched  trunks,  bearing  long,  linear  leaves  much 
like  those  of  the  Lepidodendrids ;  but  the  scars  on  the 
exterior  are  in  parallel  vertical  lines,  as  in  Fig.  281,  and 
Fig.  308,  page  300.     The  name  is  from  the  Latin  sigillum, 
seal,  in  allusion  to  the  scars. 

3.  Equiseta,  or  Horsetails.  —  The   Equiseta  of  modern 
wet  woods  are  slender,  hollow,  jointed  rushes,  called  some- 
times Scouring  Rushes.    They  often  have  a  circle  of  slender 
leaflike  appendages  at  each  joint.     The  Calamites  or  Tree 
Rushes,  which  are  referred  to  this  group,  are  peculiar  to 
the  ancient  world,  none  having  existed  since  the  Paleozoic. 
They  had  jointed  stems  like  the  Equiseta,  and  otherwise 
resembled  them.     But  they  were  often  a  score  of  feet  or 
more  in  height,   and   over  6  inches   in  diameter.      Fig. 
311,  page  300,  represents  a  portion  of  one  o£  these  plants. 


DEVONIAN    ERA.  281 

Phanerogams.  —  Others  of  the  land  plants  belong  to  the 
lowest  class  of  Flowering  Plants  or  Phanerogams,  called 
Gymnosperms  (see  page  90). 

Both  of  the  principal  orders  of  Gymnosperms  —  the 
Conifers  and  the  Cycads  —  seem  to  be  represented  in  the 
Devonian.  Some  of  the  Paleozoic  genera  appear  to  be  in 
some  respects  intermediate  between  the  two  orders,  and 
there  is  some  doubt  to  which  they  should  be  referred. 
The  fossils  are  impressions  of  leaves  and  portions  of  the 
trunk  or  branches. 

ANIMALS. 

The  early  Devonian  was  the  coral  period  of  the  ancient 
world.  In  no  age  before  or  since  have  coral  reefs  of 
greater  extent  been  formed. 

The  Molluscoid  Brachiopods  still  predominated  over 
the  Mollusks,  though  Lamellibranchs  and  Gastropods  were 
more  abundant  than  in  the  Silurian.  A  new  type  of  Ceph- 
alopods  commenced  in  the  Lower  Devonian.  Hitherto, 
the  partitions  or  septa  in  the  shells,  straight  or  coiled,  were 
flat  or  simply  concave ;  but  in  the  new  genus  Gf-oniatites 
the  margin  of  the  septum  is  crumpled  into  one  or  more 
deep  flexures.  The  name  is  from  the  Greek  <ycovLa,  angle. 
Fig.  293  (page  283)  represents  one  of  the  species,  and 
Fig.  293  a  shows  some  of  the  flexures  along  the  margin  of 
the  shell. 

Trilobites  continued  to  be  the  dominant  group  of  Crus- 
taceans, though  less  abundant  than  in  the  Silurian.  The 
earliest  of  the  order  of  Decapods  (the  order  now  repre- 
sented by  Lobsters,  Crabs,  etc.)  appeared  in  the  Devonian 
era.  The  earliest  species  were  Macrurans,  the  higher 
group  of  Brachyurans  (Crabs)  appearing  much  later. 
Land  Arthropods  were  represented  by  Insects  and  Myrio- 
pods  ;  the  wings  of  some  species  of  Insects  having  been 
reported  from  the  Devonian  of  New  Brunswick,  and  two 
species  of  Myriopods  having  been  described  from  the  Old 
Red  Sandstone  of  Scotland. 


282 


HISTORICAL   GEOLOGY. 


The  increase  of  Fishes  in  number  of  species  and  diversity 
of  types  forms  the  most  marked  characteristic  of  the  era 
The  appearance  of  Amphibians  is  an  important  step  o 
progress. 

Coelenterates.  —  Figs.  283,  284,  are  two  species  of  Cya 
thophylloid  corals  from  the  Corniferous.     Both  are  found 
at  the  Falls  of  the  Ohio,  where  the  latter  species,   Cya 
thophyllum  rugosum,  forms  very  large  masses.     Fig.  285 
is  a  species  of  Favosites  from  the  same  locality,  occurring 
also  in  Europe.     Figs.  286,  287,  are  small  corals,  probably 
belonging  to  the  group  of  Alcyoniarians. 

FIGS.  283-287. 


280 


ANTHOZOANS:  Fig.  288,  Zaphrentis  Raflnesquii;  284,  284  a,  Cyathophyllum  rugosum 
285,  Favosites  Goldfussi;  286,  Syringopora  Maclurii ;  28T,  Komingeria  cornuta.  Al 
from  the  Corniferous  period. 

Molluscoids. — Figs.  288-290  are  Brachiopods  of  the 
Hamilton  period. 

Mollusks. —  Figs.  291,  292,  are  Hamilton  Lamellibranchs. 
Fig.  293  is  a  Cephalopod,  a  species  of  Groniatites,  from  the 
same  formation.  Fig.  293  a  is  a  view  of  a  part  of  the  mar- 
howing-  the  crumpled  edges  of  the  septa. 


gin  of  the  shell,  showing 


Arthropods.  —  Fig.  294  is  one  of  the  most  common  spe- 
cies of  Trilobites  of  the  Hamilton.  Remains  of  Insects 
have  been  found  in  beds  supposed  to  be  of  the  Hamilton 
period,  at  St.  John,  New  Brunswick.  A  wing  of  a 
gigantic  species  of  May-fly  is  represented  in  Fig.  295. 


• 


DEVONIAN   ERA. 


283 


The  earliest  Myriopods  thus  far  discovered  are  from  the 
Old  Red  Sandstone  of  Scotland. 


•PIGS.  288-294. 


BRACHIOPODS:  Fig.  288,  Atrypa  aspera;  289,  Spirifer  pennatus;  290,  Chonetes  setigerus. 
—  LAMELLIBRANOHS  :  Fig.  291,  Grammysia  bisulcata ;  292,  Microdon  bellistriatus.  — 
CEPHALOPOD:  Figs.  293,  293  a,  Goniatites  Vanuxemi.  —  TRILOBITE  :  Fig.  294,  Phacops 
rana.  All  from  Hamilton  group. 

Vertebrates.  —  The  Fishes  of  the  Devonian  belong  to 
four  subclasses  :  —  1,  Selachians  ;  2,  Placoderms  ;  3,  Gran- 


284 


HISTORICAL   GEOLOGY. 


These  groups  have  been  defined  on 


FIG.  295. 


oids;  4,  Dipnoans. 
pages  81-84. 

The  Selachians,  or  Sharks,  belong,  for  the  most  part,  to 
the  family  of  Cestracionts,  in  which  the  mouth  has  a  pave- 
ment of  broad,  flat-crowned  teeth  for  grinding,  as  shown 
in  Figs.  129-131,  on  paga  82.  There  were  species  as 

large  as  the  largest  of  modern 
time.  Fig.  296  represents  a 
fin  spine  of  a  shark,  two  thirds 
its  actual  size,  from  the  Cor- 
niferous  beds  of  New  York. 

The  Placoderms  are  an  ex- 
tremely aberrant  group,  known 
exclusively  as  Silurian  and  De- 
vonian fossils.  Some  of  them 
are  represented  in  Figs.  297-300.  Figs.  297-299  are 
Fishes  from  the  Old  Red  Sandstone  of  Great  Britain. 
Fig.  300  is  a  gigantic  Placoderm  from  Ohio,  named  by 

FIG.  296. 


INSECT  :  wing  of  Platephemera  antiqua. 


SELACHIAN  :  fin  spine  of  Mackseracanthus  sulcatus,  x  §. 

Newberry  DinichtJiys  (Greek  Se^o'?,  terrible,  t'x#tfc,  fish), 
which  had  a  head  four  feet  wide. 

As  the  Placoderms  are  known  only  in  fossil  condition, 
their  true  nature  is  somewhat  problematical.  Some  of 
them,  as  CepTialaspis  and  Pterichthys  (Figs.  297,  298), 
appear  to  have  had  no  lower  jaw  (at  least,  none  capable 
of  fossilization).  It  is  doubtful  whether  they  were  truly 
Fishes.  Others,  as  Coccosteus  and  the  gigantic  Dinich- 
tJiys (Figs.  299,  300),  had  well-developed  jaws,  and  are 
believed  by  many  paleontologists  to  have  been  an  aberrant 
group  of  Dipnoans. 

One  of  the  G-anoids  is  shown  in  Fig.  301.     The  Ganoids 


DEVONIAN    ERA. 


285 


PLACODERMS  :  Fig.  29T,  Cephalaspis  Lyelll,  x|;  29T  a,  6,  scales  of  same;  298,  Pterichthys 
Milled,  x  | ;  299,  Coccosteus  decipiens,  x  $ ;  300,  Dinichthys  Hertzeri.  front  view  of 
jaws,  x  &. 


286 


HISTORICAL   GEOLOGY. 


are  now  represented  by  only  a  few  species,  among  which 
is  the  Gar  Pike  of  North  American  lakes  and  rivers. 

The  Dipnoans  are  in  many  respects  similar  to  the 
Ganoids,  but  they  show  a  close  relation  to  the  Am- 
phibians in  the  structure  of  the  heart  and  of  the  skull. 
They  are  at  present  even  less  numerous  than  the  Ganoids. 
One  of  the  Devonian  Dipnoans  is  represented  in  Fig.  302. 
The  figure  shows  the  vertebrated  (heterocercal)  tail. 
A  vertebrated  tail  (heterocercal  or  diphy cereal)  was 

FIGS.  301,  302. 


801a 


GANOID  :  Fig.  301,  Holoptychius,  x  f ;  301  a-,  scale  of  same.  —  DIPNOAN  :  Fig.  302,  Dipterus 
macrolepidotus,  x  £ ;  302  a,  scale  of  same. 

generally  characteristic  of  Paleozoic  Fishes,  whether 
Selachians,  Ganoids,  or  Dipnoans.  The  vertebrated 
character  of  the  tail  has  been  retained  by  Selachians  and 
Dipnoans  to  the  present  time  ;  but  most  of  the  Ganoids 
after  the  Paleozoic  have  the  tail  homocercal. 

An  impression  supposed  to  be  the  track  of  an  Amphibian 
was  found  in  1896,  in  the  Upper  Devonian  rocks  of  western 
Pennsylvania.  This  is  the  most  ancient  representative  yet 
discovered  of  the  classes  of  Vertebrates  above  Fishes. 


DEVONIAN   ERA. 


28T 


GENERAL  OBSERVATIONS. 


Geography.  —  During  the  Silurian,  there  had  been  a 
gradual  gain  of  dry  land,  extending  the  Archaean  con- 
tinent southward  (page  272).  This  gain  continued 
through  the  Devonian,  so  that  the  formations  of  the  next 
era,  the  Carboniferous,  extend  only  a  short  distance  north 


FIG.  303. 


Map  of  part  of  North  America  at  the  commencement  of  the  Carboniferous  era. 

of  the  southern  boundary  of  New  York.  The  seashore 
was  thus  being  set  farther  and  farther  southward  with  the 
successive  periods.  The  Cincinnati  Island  became  con- 
nected with  the  mainland,  becoming  the  extremity  of  a 
peninsula  extending  southeastward  from  northern  Illi- 
nois. The  Eastern  Interior  sea  thus  acquired  more  dis- 


288  HISTORICAL   GEOLOGY. 

tinctly  the  character  of  a  bay.  The  Tennessee  Island  be- 
came submerged.  The  map,  Fig.  303,  illustrates  the  geo- 
graphical progress  during  the  Devonian. 

The  formations  have  their  greatest  thickness  along  the 
Appalachian  region,  in  the  Devonian  era,  as  in  the  Silu- 
rian. And  both  this  fact  and  the  succession  of  different 
kinds  of  strata  lead  to  the  general  conclusions  stated  on 
page  275.  The  Devonian  age  passed  quietly  for  the 
larger  part  of  the  North  American  continent,  without  any 
tilting  of  the  rocks ;  yet  not  without  wide,  though  small, 
changes  of  level,  varying  the  limits  and  depth  of  the 
Interior  sea,  such  changes  of  level  and  of  limits  being 
indicated  by  the  varying  limits  of  the  rocks,  all  of  which 
are  of  marine  origin.  This  quiet  was  not  interrupted 
between  the  Devonian  and  Carboniferous  eras,  so  far  as 
yet  discovered,  except  to  the  northeast  in  the  region  of 
New  Brunswick,  Nova  Scotia,  and  northeastern  Maine. 
There  an  upturning  and  flexing  of  the  beds  occurred,  and, 
as  a  result,  some  mountain-making. 

In  Europe,  also,  the  Devonian  and  Carboniferous  strata 
are  conformable,  with  only  slight  local  exceptions. 

Life. — The  great  features  of  the  Devonian  age  are 
the  occurrence  of  forests  of  Acrogens  and  Gymnosperms ; 
the  increasing  number  of  Insects  and  the  first  appearance 
of  Myriopods,  among  terrestrial  Arthropods;  and  the 
great  abundance  and  variety  of  Fishes,  and  the  first  ap- 
pearance of  Amphibians. 

That  Acrogens  should  have  appeared  in  the  Silurian 
and  Devonian,  while  no  traces  have  been  found  of  the 
more  lowly  organized  terrestrial  plants,  which,  according 
to  the  theory  of  evolution,  might  have  been  expected  to 
precede  the  Acrogens,  will  not  appear  strange  when  it  is 
remembered  that  the  Acrogens  are  the  lowest  plants 
which  contain  wood  in  their  tissues.  A  Seaweed,  in  spite 
of  the  perishable  nature  of  its  tissues,  may  readily  be  pre- 
served as  a  fossil,  since  the  station  in  which  it  lives  affords 
the  opportunity  for  it  to  be  buried  before  it  has  time  to 


DEVONIAN  BRA.  289 

decompose.  But  a  woodless  terrestrial  plant  can  be  pre- 
served as  a  fossil  only  by  a  very  exceptional  combination 
of  circumstances. 

That  Gymnosperms  should  have  been  the  earliest  of 
Phanerogams  is  of  course  precisely  what  would  be  ex- 
pected. The  step  of  progress  from  Acrogens  to  Gymno- 
sperms is  a  short  one. 

The  fact  that  Vertebrates  should  have  commenced  in 
the  Silurian  and  Devonian  with  somewhat  highly  organ- 
ized forms,  is  a  case  somewhat  analogous  with  that  of  the 
Acrogens.  According  to  the  theory  of  evolution,  the 
primitive  Vertebrates  should  have  been  creatures  allied  to 
the  Leptocardians.  But  Leptocardians  (as  represented  by 
Ampliioxus)  have  neither  bones,  teeth,  scales,  nor  fin  spines 
—  nothing,  in  fact,  capable,  under  any  ordinary  conditions, 
of  being  preserved  in  fossil  condition.  The  class  of 
Marsipobranchs  seems  not  much  better  fitted  for  fossiliza- 
tion,  though  the  living  members  of  the  class  do  have  little 
teeth  implanted  in  the  mucous  membrane  of  the  mouth, 
which  might  be  preserved  in  scattered  condition.  When 
a  Vertebrate  has  acquired  sufficient  skeletal  development 
to  have  a  good  chance  of  preservation,  it  is  already  a  Fish. 
The  Selachians,  though  showing  some  noteworthy  features 
of  high  grade,  are  the  Fishes  which  most  resemble  the  Mar- 
sipobranchs, and  which  would  be  expected  to  be  the  earliest 
of  true  Fishes.  The  Teleosts,  now  the  most  abundant  of 
Fishes,  are  wanting  in  Paleozoic  and  early  Mesozoic  time. 
As  the  most  specialized  of  Fishes,  it  would  naturally  be 
expected  that  they  would  be  a  late  development. 

Economic  Products ;  Mineral  Oil  and  Gas.  —  The  oil 
wells  of  Enniskillen,  Canada,  as  already  stated,  are  in 
the  Corniferous;  but  the  "oil  horizon"  of  Pennsylvania, 
the  most  important  in  North  America,  belongs  to  the 
Upper  Devonian.  The  oil  region  forms  a  belt  about  40 
miles  wide,  extending  across  western  Pennsylvania,  from 
Monongalia  County,  West  Virginia,  to  Allegany  County, 
New  York.  This  belt  contains  many  productive  areas,  and 


290  HISTORICAL   GEOLOGY. 

hundreds  of  oil  wells.  In  1891  the  wells  near  Bradford,  in 
McKean  County,  yielded  nearly  5J  millions  of  barrels  of 
oil ;  those  of  Allegheny  County,  in  which  Pittsburg  is 
situated,  yielded  over  10J  millions ;  and  all  western  Penn- 
sylvania nearly  32  millions.  All  the  other  oil  regions  of 
the  United  States  yielded  in  1891  about  22  millions,  and 
of  this  17J  millions  were  from  Ohio.  A  barrel  holds 
42  gallons.  The  rock  to  which  the  Pennsylvania  wells 
descend  is  usually  a  coarse  and  very  porous  sandstone  ; 
the  oil  is  in  its  pores.  It  is  supposed  by  most  writers  on 
the  subject  that  the  oil  in  the  "oil  sands  "was  derived 
from  subjacent  black  or  carbonaceous  shales,  like  the 
Genesee  or  Marcellus,  by  means  of  a  gentle  heating  of 
the  rocks  during  a  period  of  upturning,  and  that  it 
became  condensed  in  the  pores  or  cavities  of  the  rocks 
above.  Such  shales,  like  coal,  do  not  contain  the  oil,  at 
least  not  in  large  quantity ;  but  they  contain  hydrocar- 
bon compounds  which  yield  oil  when  heated.  But  others 
have  thought  that  the  "  oil  sands "  originally  contained 
the  vegetable  or  animal  debris  from  which  the  contained 
oil  was  made  by  decomposition.  A  third  view  is  that  the 
oil  has  ascended  into  the  porous  sandstones  by  hydrostatic 
pressure  from  underlying  shales  in  which  it  was  formed. 
On  any  view,  the  oil  is  derived  directly  or  indirectly 
from  the  decomposition  of  organic  materials.  The  gas 
comes  from  the  same  regions  as  the  oil.  But  it  appears 
to  be  mostly  obtained  from  anticlinal  belts,  since  it  rises 
above  the  heavier  oil  and  water  contained  in  the  porous 
strata  to  the  highest  parts  of  those  strata. 

III.   CARBONIFEROUS  ERA. 

GENERAL   CHARACTERISTICS:    SUBDIVISIONS. 

The  Carboniferous  era  was  remarkable,  in  general,  for:  — 
1.  A  low  elevation   of   large   areas   of   the  continents 
above   the   sea   level,  alternating   with   shallow  submer- 
gences of  the  same. 


CARBONIFEROUS   ERA.  291 

2.  Extensive  marshy  or  fresh-water  areas  over  large 
portions  of  these  low  continents. 

3.  Luxuriant  vegetation,  covering  the  land  with  forests 
and  jungles. 

4.  A  great  increase  in  terrestrial  animal  life  —  Snails, 
Scorpions,  Spiders,  Centipedes,  Insects,  over  the  land,  and 
Amphibians  in  the  marshes.     In  the  closing  period  of  the 
era,  true  Reptiles  appeared. 

But,  while  having  these  as  its  main  characteristics,  it 
was  not  an  age  of  continuous  verdure.  There  was,  first,  a 
long  period  —  the  jSubcarboniferous  —  in  which  the  land 
was  largely  beneath  the  sea;  for  limestone,  full  of  marine 
fossils,  is  the  prevailing  rock,  and  there  are  but  few,  and 
mostly  thin,  coal  beds  intercalated  among  the  sandstones 
and  shales.  This  period  was  followed  by  the  Carbonifer- 
ous, or  that  of  the  true  Coal  Measures.  Yet,  even  in  this 
middle  period  of  the  era,  there  were  alternations  of  sub- 
merged with  emerged  continents,  long  times  of  dry  and 
marshy  lands  luxuriantly  overgrown  with  shrubbery  and 
forest  trees,  intervening  between  other  long  times  of  great 
continental  seas.  Then  there  was  a  closing  period  —  the 
Permian,  —  in  which  the  ocean  prevailed  again,  though 
with  narrower  limits  than  in  the  Subcarboniferous  ;  for 
the  rocks  are  mainly  of  marine  origin. 

The  Carboniferous  era  and  period  were  so  named  from 
the  fact  that  most  of  the  great  coal  beds  of  the  world 
originated  during  their  progress.  The  term  Permian  was 
given  to  the  rocks  of  the  third  period  by  Murchison,  De 
Verneuil,  and  Keyserling,  from  a  region  of  Permian  rocks 
in  Russia,  the  ancient  country  of  Permia,  a  part  of  which 
now  constitutes  the  government  of  Perm. 

DISTRIBUTION  OF  CARBONIFEROUS  ROCKS. 

The  Carboniferous  areas  on  the  map  of  the  United 
States  (page  235)  are  the  dark  areas ;  the  heavily  cross- 
lined  areas  being  the  Subcarboniferous;  the  pure  black, 
the  Carboniferous  and  Permian. 


292 


HISTORICAL   GEOLOGY. 


The  following  are  the  positions  of  the  several  great  coal 
areas  in  North  America  :  — 

1.  Atlantic  Border  Region.  —  1.  The  Nova  Scotia  and 
New  Brunswick  area. 


2.  The  Rhode  Island  area,  extending  from  Newport  in 
Rhode  Island  northward  into  Massachusetts. 

2.  Appalachian  and  Interior  Region.  —  1.  The  great 
Appalachian  area,  extending  from  the  southern  border  of 
New  York  southwestward  to  Alabama,  covering  the  larger 
part  of  Pennsylvania,  half  of  Ohio,  part  of  Kentucky  and 


CARBONIFEROUS   ERA.  293 

Tennessee,  and  a  portion  of  Alabama.  To  the  northeast 
in  Pennsylvania  this  coaf  held  is  much  broken  into 
patches,  as  shown  in  the  accompanying  map  of  a  part 
of  the  state,  the  black  areas  being  those  of  the  coal 
district. 

2.  The  Michigan  area,  covering  the  central  part  of  the 
state  of  Michigan. 

3.  The  Illinois-Indiana  area,  covering  much  of  Illinois, 
and  part  of  Indiana  and  Kentucky. 

4.  The  Iowa-Texas  area,  covering  part  of  Iowa,  Nebraska, 
Missouri,  Kansas,  Arkansas,  and  northern  Texas. 

3.  Arctic  Region.  —  On  Melville  Island,  and  other 
islands  between  Grinnell  Land  and  Banks  Land,  mostly 
north  of  latitude  70°. 

Besides  these,  there  is  a  small  barren  Carboniferous  area 
about  Worcester,  Massachusetts,  and  much  more  extensive 
barren  regions  about  the  slopes  and  summits  of  the  Rocky 
Mountains,  around  the  Great  Salt  Lake  in  Utah,  and  in 
California  —  the  workable  coal  beds  of  the  Rocky  Moun- 
tain region  and  Pacific  slope  being  Cretaceous  or  Ter- 
tiary. 

The  areas  of  the  Coal  Measures  in  North  America  have 
been  estimated  as  follows  :  — 

1.  Nova  Scotia  and  New  Brunswick     .  18,000  square  miles. 

2.  Rhode  Island        .        .        .         .  .  500          "         " 

3.  Appalachian 65,000 

4.  Michigan       .        .      ".        .        .  .        7,000          "         " 

5.  Illinois-Indiana      .  v    •    ,     '.'•••"*  48,000          "         " 

6.  Iowa-Texas  .....        .  .      98,000          "        " 

But  of  these  the  workable  portion  probably  does  not 
exceed  120,000  square  miles. 

Carboniferous  strata  occur  also  in  Great  Britain  and 
various  parts  of  Europe*.  The  beds  in  England  (as  shown 
in  map,  Fig.  305)  are  distributed  over  an  area  between 
South  Wales  on  the  west  and  the  Newcastle 'basin  on  the 
northeast  coast.  The  most  important  for  coal  are  the 
South  Wales  region  ;  the  Lancashire  district,  bordering  on 


294  HISTORICAL   GEOLOGY. 

Manchester  and  Liverpool  °,  the  Yorkshire,  about  Leeda 
and  Sheffield ;  and  the  Newcastle.  In  South  Wales  the 
thickness  of  the  Coal  Measures  is  7000  to  12,000  feet,  with 
more  than  100  coal  beds,  70  of  which  are  worked. 

Scotland  has  some  small  areas  between  the  Grampian 
range  on  the  north  and  the  Lammermuirs  on  the  south ; 
and  Ireland,  several  coal  regions  of  large  extent. 

The  coal  fields  of  the  continent  of  Europe  that  are 
most  worked  are  the  Belgian,  bordering  on  and  passing 
into  France.  Germany  contains  small  coal-bearing  areas 
in  Rhenish  Prussia,  Westphalia,  and  Silesia.  Russia  in 
Europe  affords  very  little  coal,  although  rocks  of  the 
Carboniferous  era  cover  large  portions  of  the  surface. 

The  area  of  the  Coal  Measures  in  Great  Britain  and 
Ireland  is  about  12,000  square  miles ;  in  Spain,  4000  ;  in 
France,  2000  ;  Germany,  1800 ;  Belgium,  518. 

Coal  beds  of  Carboniferous  age  occur  also  in  China  and 
in  Spitzbergen.  Valuable  coal  beds  of  Permian  age  occur 
in  India  (in  the  Lower  Gondwana  series)  and  in  Australia. 

Valuable  coal  beds  are  not  found  in  any  rocks  older 
than  those  of  the  Carboniferous  era,  although  black  car- 
bonaceous shales  are  not  uncommon  even  in  the  Lower 
Silurian.  They  occur,  however,  in  various  Mesozoic  for- 
mations, and  also  in  the  Cenozoic,  but  not  on  so  extensive 
a  scale  as  in  the  Carboniferous  formations. 

KINDS  OP  ROCKS. 

1.  Subcarboniferous  Period.  —  The  Subcarboniferous 
strata  in  the  Central  Interior  region  are  mainly  limestone  ; 
and,  as  the  limestone  abounds  in  many  places  in  Crinoidal 
remains,  the  rock  is  often  called  the  Crinoidal  Limestone. 
In  the  Appalachian  region,  in  southwestern  Virginia,  Ten- 
nessee, and  Alabama,  the  rock  is  also  in  large  part  lime- 
stone, and  has  great  thickness ;  but  farther  north,  in  West 
Virginia  and  Pennsylvania,  it  is  mostly  a  sandstone  or  con- 
glomerate (Pocono  group),  overlain  by  shaly  sandstones  and 
shales  of  reddish  and  other  colors  CMauch  Chunk  group) 


CARBONIFEROUS   ERA. 


295 


—  the  whole  having  a  maximum  thickness  of  4000  to 
5000  feet.  In  the  Atlantic  Border  region,  in  Nova  Scotia, 
the  rocks  are  mostly  reddish  sandstone  and  shale,  with 


FIG.  305. 


Geological  map  of  England  and  southern  Scotland.  The  small  white  areas  are  those  of 
igneous  rocks.  The  areas  numbered  1  are  Cambrian  and  Silurian  ;  2,  Devonian ;  8,  Sub- 
carboniferous  and  Millstone  Grit;  4,  Coal  Measures;  5,  Permian;  6,  Triassic ;  7,  Lias; 
8,  Oolite ;  9,  Wealden  ;  10,  Cretaceous  (exclusive  of  Wealden) ;  11,  Tertiary.  A  is  London  ; 
B,  Liverpool ;  C,  Manchester  :  D,  Newcastle  :  E,  Gla«<row 


296  HISTORICAL   GEOLOGY. 

some  limestone  —  the  estimated  thickness  6000  feet.  In 
Michigan  and  Ohio  the  Subcarboniferous  rocks  yield  brines, 
which  are  used  for  the  manufacture  of  salt. 

The  prevailing  rock  in  Great  Britain  and  Europe  is  a 
limestone,  called  the  Mountain  Limestone.  In  Northum- 
berland and  Scotland,  the  Subcarboniferous  consists  chiefly 
of  sandstones,  and  contains  productive  coal  beds. 

2.  Carboniferous  Period.  —  The  base  of  the  series  of 
Carboniferous  rocks  is  generally  formed  by  a  hard,  gritty 
sandstone  or  conglomerate,  called  in  England  the  Millstone 
Grit  from  its  frequent  use  for  millstones.  A  similar  rock 
in  Pennsylvania  is  called  the  Pottsville  Conglomerate.  In 
the  center  of  the  Anthracite  region  it  attains  a  thickness 
of  800  to  1700  feet,  but  thins  out  westward.  In  parts  of 
Pennsylvania  the  Pottsville  Conglomerate  contains  beds 
of  coal.  In  Nova  Scotia,  the  Millstone  Grit  is  5000  to 
6000 -feet  thick. 

This  conglomerate  is  overlain  by  the  Coal  Measures 
proper.  The  rocks  of  the  Coal  Measures  are  sandstones, 
shales,  conglomerates,  and  occasionally  limestones  ;  and 
they  are  so  similar  to  the  rocks  of  the  Devonian  and 
Silurian  ages  that  they  cannot  be  distinguished  except  by 
the  fossils.  They  occur  in  various  alternations,  with  an 
occasional  bed  of  coal  between  them.  The  coal  beds,  taken 
together,  generally  make  up  not  more  than  one  fiftieth  of 
the  whole  thickness ;  that  is,  there  are  i-n  general  50  feet 
or  more  of  barren  rock  to  1  foot  of  coal.  The  maximum 
thickness  in  Pennsylvania  is  nearly  3000  feet;  in  Nova 
Scotia,  about  5000  feet. 

Although  coal  beds  may  occur  in  any  part  of  the  Coal 
Measures,  they  are  often  very  unequally  distributed  through 
the  series.  In  Pennsylvania  three  divisions  of  the  series 
are  recognized:  (1)  the  Lower  Productive  Measures,  (2) 
the  Lower  Barren  Measures,  (8)  the  Upper  Productive 
Measures.  The  second  of  these  divisions  contains  only 
thin  and  insignificant  coal  beds.  The  Upper  Barren 
Measures,  overlying  the  Upper  Productive  Measures,  be- 


CARBONIFEROUS    EKA. 


297 


long  to  the  Permian.  In  the  coal  field  of  South  Wales, 
the  Coal  Measures  are  similarly  divided  into  two  parts 
by  a  great  thickness  of  barren  sandstone. 

The  limestone  strata  are  more  numerous  and  extensive 
in  the  Central  Interior  region  than  in  the  Appalachian; 
west  of  the  states  of  Missouri  and  Kansas,  limestone  is  the 
prevailing  rock.  In  Kansas  and  in  West  Virginia  the 
rocks  afford  brines. 

Beds  of  argillaceous  iron  ore  or  clay  ironstone  are  very 
common  in  coal  districts,  so  that  the  same  region  affords 
ore  and  the  coal  for  smelting  it.  Some  of  the  largest  iron 
works  in  the  world,  on  both  sides  of  the  Atlantic,  occur 

FIG.  806. 


Section  of  a  portion  of  the  Coal  Measures  at  the  Joggins,  Nova  Scotia,  having  erect  stump  . 
and  also  roots  in  the  underclays. 

in  coal  di3tricts.  The  ore  is  usually  siderite,  or  iron  car- 
bonate (more  rarely,  limonite),  impure  from  mixture  with 
some  earth  or  clay. 

The  coal  beds  often  rest  on  a  bed  of  grajdsh  or  bluish 
clay,  called  the  underclay,  which  is  filled  with  the  roots  or 
underground  stems  of  plants.  When  this  underclay  is 
absent,  the  rock  below  is  usually  a  sandstone  or  a  shale. 
Above  the  coal  bed  the  rock  may  be  sandstone,  shale,  con- 
glomerate, or  even  limestone;  often  the  layer  next  above, 
especially  if  shaly,  is  filled  with  fossil  leaves  and  stems. 
In  some  cases,  trunks  of  old  trees  rise  from  the  coal  and 
extend  up  through  overlying  beds,  as  shown  in  Fig.  306, 
by  Dawson,  from  the  Nova  Scotia  Coal  Measures.  Occa- 


298  HISTORICAL  GEOLOGY. 

sionally,  as  in  Ohio  and  Pennsylvania,  logs  50  to  60  feet 
long  lie  scattered  through  the  sandstone  beds,  looking  as 
if  a  forest  had  been  swept  off  from  the  land  into  the  sea. 

The  coal  beds  vary  in  thickness  from  a  fraction  of  an 
inch  to  scores  of  feet,  but  seldom  exceed  8  feet,  and  are 
generally  much  thinner.  Eight  to  10  feet  is  the  thick- 
ness of  the  principal  bed  at  Pittsburg,  Pennsylvania;  50 
feet  or  more,  the  thickness  (in  some  places)  of  the  "Mam- 
moth" bed  of  the  Anthracite  region  of  Pennsylvania;  38 
feet,  that  of  one  of  the  two  great  beds  at  Pictou  in  Nova 
Scotia.  In  these  thick  beds,  and  often  also  in  the  thin 
ones,  there  are  some  intervening  beds  of  shale,  or  of  very 
impure  coal,  so  that  only  a  part  is  fit  for  burning. 

The  coal  varies  in  kind,  as  explained  on  page  25  ;  that 
yielding  only  about  5  per  cent  of  volatile  hydrocarbons, 
and  burning  with  little  flame,  being  called  anthracite  ;  and 
that  yielding  20  to  50  per  cent  of  volatile  hydrocarbons, 
and  burning  with  a  bright  yellow  flame,  bituminous  coal. 
Varieties  intermediate  between  the  typical  anthracite  and 
bituminous  coal  are  often  called  semi-bituminous  coal.  The 
coal  of  the  Pottsville,  Lehigh,  and  Wilkesbarre  regions  in 
Pennsylvania  is  anthracite;  that  of  Pittsburg  and  the  West, 
bituminous  coal;  and  that  of  part  of  the  intermediate  dis- 
trict, semi-bituminous,  as  designated  on  the  map,  page  292. 

The  coal  also  varies  as  to  the  impurities  present.  All  of 
it  contains  more  or  less  of  earthy  material,  and  this  con- 
stitutes the  ashes  and  slag  of  a  coal  fire.  Ordinary  good 
anthracite  contains  4  to  8  pounds  of  impurities  in  a 
hundred  pounds  of  coal,  and  the  best  bituminous  coals 
1  to  6.  In  some  coal  beds  there  is  much  iron  sulphide,  or 
pyrite,  and  the  coal  is  then  unfit  for  use.  It  is  seldom 
that  the  sulphide  is  altogether  absent;  it  is  the  chief  source 
of  the  sulphur  gases  that  are  perceived  in  the  smoke  or  gas 
from  a  coal  fire. 

Mineral  coal,  although  it  seldom  breaks  into  plates  unless 
quite  impure,  still  consists  of  thin  layers.  Even  the  hardest 
anthracite  is  delicately  banded,  as  seen  on  a  surface  of  f  rac- 


CARBONIFEROUS   ERA.  299 

ture  when  it  is  held  up  to  the  light.  This  structure  is  absent 
in  the  variety  called  cannel  coal,  which  is  a  bituminous  coal, 
very  compact  in  texture,  feeble  in  luster,  and  smooth  in 
fracture. 

3.  Permian  Period.  — The  upper  part  of  the  Carbonifer- 
ous formation  (Upper  Barren  Measures)  of  Pennsylvania 
and  Virginia  has  been  shown  by  its  fossil  plants,  and  that 
of  Illinois,  Kansas,  and  Texas,  by  its  Reptiles  and  Mol- 
lusks,  to  be  Permian.  The  uppermost  strata  in  the  Aca- 
dian Coal  area  also  are  Permian.  Permian  strata  occur 
also  in  the  Rocky  Mountain  region.  The  rocks  are  mostly 
reddish  and  gray  sandstones  and  shales,  with  some  impure 
limestone.  The  Permian  strata  of  Texas  have  been  in- 
cluded with  the  Triassic,  under  the  name  Red  Beds.  In 
Kansas  the  rocks  include  a  large  amount  of  limestone. 
Similar  red  and  gray  sandstones  and  shales  occur  in  Great 
Britain,  in  the  vicinity  of  several  of  the  Coal  regions,  and 
also  in  Germany  and  Russia.  The  Permian  rocks  of 
Great  Britain  were  formerly  included  with  the  Triassic 
under  the  name  New  Red  Sandstone. 

In  India  and  in  Australia,  the  Permian  formation  con- 
tains valuable  beds  of  coal. 

In  England,  India,  Australia,  South  Africa,  and  south- 
ern Brazil,  the  Permian  includes  a  conglomerate  with 
bowlders  of  great  size,  some  of  which  show  subangular 
forms  and  smoothed  and  striated  surfaces,  like  those  of 
glaciated  bowlders  (pages  164,  408).  While  some  geolo- 
gists have  not  hesitated  to  infer  the  existence  of  a  glacial 
climate  in  those  regions,  others  believe  that  a  conclusion 
so  startling  requires  confirmation. 

LIFE. 
PLANTS. 

The  plants  of  the  forests,  jungles,  and  floating  islands 
of  the  Carboniferous  age,  thus  far  made  known,  number 
nearly  2000  species.  Among  the  fossils  there  are  none 


300 


HISTORICAL   GEOLOGY. 


that  afford  satisfactory  evidence  of  the  presence  of  Angio- 
sperms.  There  were  no  Oaks,  nor  Maples,  nor  Palms  in 
the  forests,  and  the  plains  were  without  grass.  At  the 


FIGS.  307-312. 


309 


ACROGENS  :  Fig.  307,  Lepidodendron  aculeatum ;  308,  Sigillaria  oculata ;  309,  Stigmaria 
ficoides  ;  310,  Sphenopteris  Gravenhorstii ;  311,  Calamites  cannaeforinis.  —  GYMNOSPERM  : 
Fig.  312,  Trigonocarpus. 

present  day,  Angiosperms,  along  with  Conifers,  make  up 
the  great  bulk  of  our  shrubs  and  trees  ;  Palms  abound 
in  all  tropical  countries;  and  grass  covers  all  exposed 
slopes  where  the  climate  is  not  too  arid. 


CARBONIFEROUS    ERA.  301 

Cryptogams.  —  The  Carboniferous  species,  like  their 
predecessors  in  the  Devonian  age,  belonged  mostly  to 
the  following  groups  :  — 

1.  Ferns.  —  Ferns  were  very  abundant,  a  large  part  of 
the  fossils  of  a  coal  region  being  their  delicate  fronds,  or 
leaves.     A  portion  of  a  fossil  Fern  is  represented  in  Fig. 
310.     Besides  small  species,  like  the  common  kinds  of  the 
present  day,  there  were  (as  is  now  the  case  in  the  tropics) 
Tree  Ferns  —  species  that  had  a  trunk,  perhaps  20  or  30 
feet  high,  which  bore  at  top  a  radiating  tuft  of  very  large 
fronds.     Tree  Ferns,  however,  were  not  very  common  in 
the  Carboniferous  forests.     The  scars  in  fossil  or  recent 
Tree  Ferns  are  many  times  larger  than  those  of  Lepidoden- 
drids,  and  the  fossils  may  be  thus  distinguished. 

2.  Lycopods.  —  The  Lepidodendrids  appear  to  have  been 
among  the  most  abundant  of  Carboniferous  forest  trees, 
especially  in  the  earlier  half  of  the  era,  or  to  the  middle 
of  the  Coal  Measures.     They  probably  covered  both  the 
marshes  and  the  drier  plains  and  hills.     Some  of  the  old 
logs  now  preserved  in  the  strata  are  50  to  60  feet  in  length, 
strikingly  contrasting  with  the  little  Ground  Pines  of  mod- 
ern times;  and  the  pinelike  leaves  were  occasionally  a  foot 
or  more  long.     Fig:  307  shows  the  surface  markings  of 
one  of  the  species,  natural  size. 

The  SigiUaricB  were  a  very  marked  feature  of  the  great 
jungles  and  deep  forests  of  the  Coal  period.  They  grew 
to  a  height  sometimes  of  30  to  60  feet ;  but  the  trunks 
were  seldom  branched,  and  must  have  had  a  stiff,  clumsy 
aspect,  although  covered  above  with  long,  slender,  rush-, 
like  leaves.  Fig.  308  represents  a  common  species,  ex- 
hibiting the  usual  arrangement  of  the  scars  in  vertical 
lines,  and  also  indicating,  by  the  difference  between  the 
scars  of  the  right  row  and  the  others,  their  difference  of 
form  on  the  outer  surface  of* the  tree  and  beneath  the  rind. 

The  fossil  Stigmarice  are  stout  stemlike  bodies,  generally 
2  to  3  or  more  inches  thick,  having  over  the  surface  distinct 
rounded  depressions,  or  scars.  Fig.  309  is  a  portion  of 


302  HISTORICAL   GEOLOGY. 

the  extremity  of  a  stem,  showing  the  rounded  depressions, 
and  also  the  appendages  (rootlets)  whose  position,  when 
they  have  decayed  or  fallen  off,  is  marked  by  the  scars, 
and  which  are  occasionally  observed  in  place.  The  stems 
are  a  little  irregular  in  form,  and  sparingly  branched. 
They  have  been  found  spreading,  like  roots,  from  the  base 
of  the  trunk  of  a  Sigillaria,  and  sometimes  also  from  that 
of  a  Lepidodendron ;  arid  they  are  hence  regarded  as  the 
roots  or  rootstocks  of  these  trees.  They  are  an  exceed- 
ingly common  fossil,  especially  in  the  underclays  of  the 
Coal  Measures  (page  297). 

3.  Equiseta.  —  Fig.  311  represents  a  portion  of  one  of 
the  Tree  Rushes,  or  Calamites,  of  the  Equisetum,  or  Horse- 
tail group.  These  plants  were  very  abundant  in  the 
great  marshes,  through  the  whole  of  the  era.  Some  of 
them  were  20  feet  or  more  in  height,  and  10  or  12  inches 
in  diameter. 

Besides  these  Acrogens,  a  few  remains  of  Fungi  have 
been  found,  but,  as  yet,  no  remains  of  Mosses.  A  Moss, 
however,  could  only  be  preserved  as  a  fossil  under  very 
exceptional  conditions;  and  in  such  a  case  the  negative 
evidence  is  of  little  value. 

Phanerogams.  —  As  in  the  Devonian  era,  both  Conifers 
and  Cycads  were  probably  present.  Some  of  the  genera 
seem  to  show  characters  intermediate  between  these  two 
types.  - 

Trunks  of  trees,  Coniferous  in  character,  are  not  uncom- 
mon. 

There  are  also  various  nutlike  fruits  found  in  the  Car- 
boniferous strata.  One  is  represented  in  Fig.  312  (page 
300),  the  figure  to  the  left  being  that  of  the  shell,  and  the 
other  that  of  the  nut  which  it  contained.  Some  of  them 
are  two  inches  in  length.  Thejnost  of  them  were  probably 
the  fruit  of  Conifers,  but  possibly  of  Cycads. 

It  is  seen  from  the  above  that  — 

1.  The  vegetation  of  the  Carboniferous  era  consisted 
very  largely  of  Cryptogams,  or  flowerless  plants. 


CARBONIFEROUS   ERA.  303 

2.  The  flowering  plants,  or  Phanerogams,  associated 
with  the  flowerless  vegetation,  were  of  the  class  of  Gym- 
nosperms,  whose  flowers  are  simple  and  inconspicuous. 

.  3.  While,  therefore,  there  was  abundant  and  beautiful 
foliage  (for  no  foliage  exceeds  in  beauty  that  of  Ferns), 
the  vegetation  was  nearly  flowerless. 

4.  The  characteristic  Cryptogams  were  not  only  of  the 
highest  group  of  that  division  of  plants,  but  many  of  them 
exceeded  in  size  and  in  complexity  of  organization  the 
species  of  the  present  day. 

ANIMALS. 

Coelenterates.  —  Fig.  313  presents  a  view  of  the  upper 
surface  of  a  very  common  Coral  of  the  Subcarboniferous 
period  :  it  has  a  columnar  appearance  in  a  side  view. 

Echinoderms.  —  Crinoids  were  especially  numerous  in 
the  Subcarboniferous  period.  Figs.  314-316  represent 
some  of  the  species.  Figs.  314,  315,  are  Brachiate 
Crinoids.  In  the  former,  the  arms  are  perfect;  in  the 
latter,  they  have  been  broken  off.  Fig.  316  is  a  repre- 
sentative of  the  Blastoids,  a  group  which  commenced  in 
the  Upper  Silurian,  attained  its  maximum  development 
in  the  Subcarboniferous,  and  became  extinct  at  the  close 
of  the  Carboniferous  period. 

Molluscoids.  —  The  class  of  Bryozoans  included  the 
singular  screw-shaped  (or  auger-shaped)  Coral  shown  in 
Fig.  317,  and  named  Archimedes  (referring  to  Archimedes' 
screw).  The  upper,  or  inner,  surface  of  the  spiral  lamina 
shows  the  orifices  of  the  cells,  each  of  which,  when  alive, 
contained  a  minute  individual  of  the  colony  (page  70). 
These  fossils  are  common  in  some  of  the  Subcarboniferous 
limestone  strata. 

Brachiopods  were  very  abundant  through  the  Carbon- 
iferous age,  and  especially  species  of  the  genera  Spirifer 
and  Productus.  Figs.  318-321  are  of  species  from  the 
American  Coal  Measures. 


304 


HISTORICAL   GEOLOGY. 


Mollusks.  —  Fig.  322  represents  one  of  the  marine  Gas- 
tropods of  the  Coal  Measures.    Fig.  323  is  a  Pupa,  the  earli- 


FIGS.  313-323. 


ANTHOZOAN  :  Fig.  313,  Lithbstrotion  Canadense.  —  CRINOIDS  :  Fig.  314,  Woodocrinus  elegans; 
315,  Actinocrinus  proboscidialis  ;  316,  Pentremites  pyrifonnis.  —  BRYOZOAN  :  Fig.  317, 
Archimedes  Wortheni. —BRACHIOPODS:  318,  Chonetes  mesolobus  ;  319,  Productus  Ne- 
brascensis;  320,  Athyris  subtilita;  321,  Spirifer  cameratus.  —  GASTROPODS  :  322,  Pleu- 
rotomaria  tabulata ;  323,  Pupa  vetusta. 

est  yet  found  of  Land  Snails  :  it  is  from  the  Coal  Measures 
of  Nova  Scotia ;  others  have  been  found  in  Illinois.  The 
class  of  Cephalopods  was  represented  by  few  and  small 


CARBONIFEROUS  ERA. 


305 


FIG.  324. 


species  of  the  old  group  of  Orthocerata,  but  by  many  of 
the  Ammonite-like  Goniatites. 

Arthropods.  —  Trilobites,  which 
had  been  in  earlier  times  the  domi- 
nant group  of  Crustaceans,  were 
rare  in  the  Carboniferous  era,  and 
entirely  disappeared  at  its  close. 
The  Macruran  Decapods,  which 
had  commenced  in  the  Devonian, 
became  more  abundant.  One  of 
them  is  represented  in  Fig.  324. 

Arachnoids  were  represented 
by  Scorpions  (Fig.  325)  and  Spi- 
ders (Fig.  326),  the  latter  group 
making  their  first  appearance  in 
this  era.  Insects  were  represented 
by.  Myriopods  (Fig.  327)  and 
Hexapods.  Among  the  Hexapods,  the  Orthopters  were 
abundantly  represented  by  Cockroaches  (Fig.  328)  and 

FIG.  325. 


DECAPOD  :  Anthracopalaemon 
gracilis. 


L 


ARACHNOID  :  Eoscorpius  carbonarius. 

Locusts,   and  the    Pseudoneuropters  by  May-flies.      Fig. 
329  represents  an  Insect  which  is  either  a  Pseudoneuropter 


306 


HISTORICAL  GEOLOGY. 


or  a  Neuropter,  those  two  orders  being  often  undistinguish- 
able  in  fossil  condition.  The  earliest  remains  of  Hemipters 
occur  in  the  Permian.  Remains  of  Beetles  (Coleopters) 
have  been  doubtfully  reported  from  the  Subcarboniferous 
of  Silesia.  With  doubtful  exceptions,  the  higher  orders 
of  Insects,  characterised  by  passing  through  an  inactive 
pupa  stage  (complete  metamorphosis),  are  wanting  in  the 
Paleozoic. 

Vertebrates.  —  Fishes  were  numerous,  including  Selach- 
ians, Ganoids,  and  Dipnoans.     Many  of  the  Selachians 

FIGS.  326-329. 


ARACHNOID  :  Fig.  326,  Arthrolycosa  antiqua.  —  MYRIOPOD:  FIG.  327,  Xylobius  sigillarise.  — 
HEXAPODS:  Fig.  328,  wing  of  Etoblattina  venusta;  329,  Miamia  Bronsoni. 

were  of  great  size,  as  shown  by  the  fin  spines.  Fig.  331 
represents  a  small  portion  of  one  of  these  spines,  natural 
size,  from  the  Subcarboniferous  beds  of  Europe.  One  of 
the  largest  specimens  of  a  spine  of  the  same  species,  when 
entire,  must  have  been  18  inches  long.  Nearly  all  the 
Ganoids  had  vertebrated  tails,  as  shown  in  Fig.  330, 
which  represents  a  common  Permian  species. 

Amphibians  occur  throughout  the  era.  They  all  belong 
to  an  order  which  became  extinct  at  the  close  of  the 
Triassic  or  during  the  Jurassic.  Unlike  the  Frogs  and 


CARBONIFEROUS   ERA. 


307 


Salamanders,  their  skulls  had  a  complete  bony  roof  (Fig. 
384,  page  352),  which  has  suggested  the  name  Stego- 
cephala,  from  oreyo>,  to  cover,  and  /ce^aXt;,  head.  Many 
of  the  species  show  a  complicated  structure  of  the  teeth, 
the  cementum  forming  a  series  of  folds  which  penetrate 
to  a  greater  or  less  depth  into  the  dentine.  These  laby- 
rinthine teeth  have  suggested  the  name  Labyrinthodonts. 
This  peculiarity  they  share  with  many  Ganoid  Fishes.  It 


FISHES:  Fig.  330,  Pala-oniscus  Freieslebeni,  x  J ;  331,  part  of  a  spine  of  Ctenacanthus  major. 

is  shown  in  a  comparatively  simple  form  in  the  recent 
Lepidosteus  (Fig.  140,  page  84).  It  becomes  much  more 
complex  in  some  of  the  Triassic  Labyrinthodonts.  The 
earliest  traces  of  Amphibians  known  (until  the  recent 
discovery  of  Devonian  tracks,  mentioned  on  page  286) 
are  tracks  found  in  the  Subcarboniferous  beds  at  Potts- 
ville,  Pennsylvania  (Fig.  332)  ;  they  are  about  four  inches 
broad,  those  of  the  fore  feet,  as  described  by  Dr.  Lea, 
5-toed,  and  those  of  the  hind  feet  4-toed.  Fig.  333  repre- 
sents a  skeleton  of  another  species  from  the  Ohio  Coal 
Measures.  Some  of  the  related  Amphibians  from  Ohio 
are  long  and  destitute  of  limbs,  like  Snakes. 


308 


HISTORICAL  GEOLOGY, 


Reptiles  made  their  first  appearance  in  the  Permian. 
Two  orders  of  Reptiles  were  represented  :  (1)  the  Rhyn- 
chocephala,  a  group  represented  by  numerous  Permian  and 

FIGS.  832,  833. 


AMPHIBIANS  :  Fig.  332,  tracks  of  Sauropus  primsevus,  x  f ;  383,  Pelion  Lyellii. 

Mesozoic  species,  but  now  nearly  extinct,  a  single  genus 
surviving  in  New  Zealand ;  (2)  the  Theromorphs,  a  group 
confined  to  the  Permian  and  Triassic,  remarkable  for 
certain  striking  resemblances  to  Mammals,  particularly  in 
the  skull.  Fig.  334  shows  the  skull  of  one  of  the  Rhyn- 
chocephala,  from  the  Permian  of  Saxony. 


CARBONIFEROUS   ERA. 


309 


FIG.  834. 


GENERAL  OBSERVATIONS. 

Mode  of  Formation  of  the  Coal  Measures.  —  Origin  of  the 
Coal.  —  The  vegetable  origin  of  coal  is  proved  by  the 
following  facts: — 

1.  Trunks      of 
trees,  still  retain- 
ing   the    original 
form  and  part  of 
the  structure  of  the 
wood,   have   been 
found  changed  to 
mineral  coal,  both 
in  the  Carbonifer- 
ous strata  and  in 
more  modern  for- 
mations,   showing 
that    the    change 
may  and  does  take 
place. 

2.  Beds  of  peat, 

a  result  of  vegetable  growth  and  accumulation,  exist  in 
modern  marshes ;  and  in  some  cases  they  are  altered  be- 
low to  an  imperfect  coal.  (See  page  107,  on  the  formation 
of  peat.) 

3.  Remains  of  plants  —  leaves,  branches,  and  stems  or 
trunks  —  abound  in  the  Coal  Measures  ;  trunks  sometimes 
extend  upward  from  a  coal  bed  into  and  through  some  of 
the  overlying  beds  of  rock ;  roots  or  stems  abound  in  the 
underclays. 

4.  The  hardest  anthracite  contains  throughout  its  mass 
vegetable  tissues.     Professor  Bailey  examined  with  a  high 
magnifying  power  several  pieces  of   anthracite  burnt  at 
one  end,  like  Fig.  335,  taking  fragments  from  the  junc- 
tion of  the  white  and  the  black  portion,  and  readily  de- 
tected the  tissues.     Fig.  336  represents  the  ducts,  as  they 


REPTILE  :  Palaeohatteria  longicaudata. 


310 


HISTORICAL  GEOLOGY. 


appeared  in  one  case  under  his  microscope  ;  and  Fig.  337, 
part  of  the  same,  more  magnified.  Fig.  338  shows  the 
appearance  of  the  spores  of  Lycopods  (Lepidodendrids) 
much  magnified  ;  they  are  common  in  coal. 


FIGS.  335-33T. 


FIG.  338. 


Vegetable  tissues  in  anthracite. 

Decomposition  of  Vegetable  Material.  —  The  mineral  coal 
of  the  Coal  Measures  consists  (impurities  excluded)  of 
65  to  93  per  cent  of  carbon,  along  with  2  to  9  of  hydro- 
gen, and  2  to  17  of  oxygen ; 
and  woody  material,  whether 
of  Conifers,  Ferns,  Lycopods, 
or  Equiseta,  consists  of  about 
45  per  cent  of  carbon,  6  of 
hydrogen,  and  49  of  oxygen. 
To  change  the  vegetable  ma- 
terial to  coal,  it  is  necessary 
to  get  rid  of  part  of  the  oxy- 
gen and  hydrogen.  Vegetable 
matter  decomposing  in  the 
open  air  —  like  wood  burnt 

Spores  and  part  of  a  sporangium  of  Lepido-       jn  an  open  fire is  COmplete- 

dendron  in  bituminous  coal  of  Ohio,  x  TO.  .  , .        ,  ,  ™ 

ly  oxidized,  and  passes  on  as 

water  vapor  and  carbon  dioxide.  Both  the  oxygen  of  the 
air  and  that  of  the  wood  take  part  in  the  combustion  or 
decomposition.  But,  if  the  former  is  more  or  less  excluded 
by  a  covering  of  earth  or  of  water  (as  in  a  swamp),  the 


CARBONIFEROUS  ERA.  311 

combustion  is  incomplete,  and  coal  may  result,  consisting 
of  the  unconsumed  carbon  combined  with  some  hydrogen 
and  oxygen. 

The  actual  loss,  by  weight,  in  conversion  into  bitumi- 
nous coal,  is  at  least  three  fifths  of  the  wood,  and,  in  con- 
version into  anthracite,  three  fourths.  Adding  to  this  loss 
that  from  compression,  by  which  the  material  is  brought 
to  the  density  of  mineral  coal,  the  whole  reduction  in  bulk 
is  not  less  than  four  fifths  for  the  former,  and  seven  eighths 
for  the  latter.  In  other  words,  it  would  take  5  cubic  feet 
of  vegetable  matter  to  make  1  of  bituminous  coal,  and  8 
feet  to  make  1  of  anthracite. 

Impurities  in  Coal.  —  The  coal  thus  formed  derived  some 
silica  and  other  earthy  ingredients  from  the  wood  itself, 
including  probably,  in  the  case  of  the  Lepidodendrids, 
some  alumina,  since  this  earth  exists  in  the  ash  of  modern 
Lycopods.  From  this  source  the  best  coal  received  some 
earthy  impurities,  while  the  poorer  coals  contain,  in  addi- 
tion, clay  or  earthy  material  carried  over  the  marshes  by 
the  waters  or  winds.  Sulphur  is  a  common  impurity;  it 
usually  occurs  combined  with  iron,  forming  pyrite,  or  sul- 
phide of  iron. 

Accumulation  and  Formation  of  Coal  Beds. — The  ori- 
gin of  coal  beds  was,  then,  as  follows :  The  plants  of  the 
great  marshes  and  shallow  lakes  of  the  Carboniferous 
period,  the  latter  with  their  floating  islands  of  vegetation, 
continued  growing  for  a  long  period,  dropping  annually 
their  leaves,  and  from  time  to  time  decaying  stems  or 
branches,  until  a  thick  accumulation  of  vegetable  remains 
was  formed  —  probably  5  feet  in  thickness  for  a  one-foot 
bed  of  bituminous  coal.  The  bed  of  material  thus  pre- 
pared over  the  vast  wet  areas  of  the  continent  early  com- 
menced to  undergo  at  bottom  that  slow  decomposition  the 
final  result  of  which  is  mineral  ccal.  But  the  alternation 
of  the  coal  beds  with  sandstones,  shales,  conglomerates, 
and. limestones,  shows  that  the  long  period  of  verdure  was 
followed  by  a  period  of  overflowing  waters,  which  dis- 


312  HISTORICAL   GEOLOGY. 

tributed  sands,  pebbles,  earth,  or  the  remains  of  the  skele- 
tons of  aquatic  organisms,  over  the  old  marsh",  till  scores 
or  hundreds  of  feet  in  depth  of  such  deposits  had  been 
made.  In  the  Central  Interior  region  of  North  America, 
the  overflowing  waters  were  generally  marine,  as  is  proved 
by  marine  fossils  in  the  strata.  Thus  the  bed  of  vegetable 
material  was  buried ;  and  under  this  condition  the  process 
of  decomposition  and  change  to  mineral  coal  went  forward 
to  its  completion  ;  it  had  the  smothering  influence  of  the 
burial,  as  well  as  the  presence  of  water,  to  favor  the  process. 

Climate  of  the  Age.  — The  wide  distribution  of  the 
coal  regions  over  the  globe,  from  the  tropics  to  remote 
Arctic  lands,  and  the  general  similarity  of  the  vegetable 
remains  in  the  coal  beds  of  these  distant  zones,  prove  that 
there  was  a  general  uniformity  of  climate  over  the  globe 
in  the  Carboniferous  period,  or  at  least  that  the  climate 
was  nowhere  colder  than  warm-temperate.  Besides,  corals 
and  shells  existed  during  the  Subcarboniferous  period 
in  Europe,  the  United  States,  and  the  Arctic  regions 
within  20°  of  the  North  Pole,  and  so  profusely  as  to  form 
thick  limestones  out  of  their  accumulations ;  and  some 
Arctic  species  are  identical  with  those  of  Europe  and 
America.  The  ocean's  waters,  even  in  the  far  north, 
were,  therefore,  warm  compared  with  those  of  the  modern 
temperate  zone,  and  probably  quite  as  warm  as  the  coral- 
reef  seas  of  the  present  age,  which  lie  mostly  between  the 
parallels  of  28°  either  side  of  the  equator.  This  uniform 
warm  climate  appears  to  have  characterized  the  whole 
of  the  Paleozoic,  no  clearly  defined  climatic  zones  being 
indicated  until  a  later  period.  Whether  the  bowlder 
beds  of  the  Permian  (page  299)  will  require  modification 
of  current  opinions  regarding  Paleozoic  climate,  is  at 
present  matter  of  doubt. 

Atmosphere. — The  atmosphere  contained  a  larger  amount 
than  now  of  carbon  dioxide  —  the  gas  from  which  plants 
derive  their  carbon.  The  mineral  coal  of  the  world 
is  approximately  a  measure  of  the  amount  of  carbon 


CARBONIFEROUS   ERA.  313 

dioxide  permanently  withdrawn  from  the  atmosphere  by 
the  coal  plants.  The  growth  of  the  flora  of  that  age 
was  a  means  of  purifying  the  atmosphere,  so  as  to  fit 
it  for  the  higher  terrestrial  life  that  was  afterward  to 
possess  the  world.  The  amount  of  carbon  dioxide  lost 
by  the  atmosphere  in  the  formation  of  carbonate  of  lime 
and  other  carbonates,  in  the  course  of  geological  time, 
is  even  greater  than  the  loss  by  means  of  vegetation. 
(See  page  236.) 

Again,  the  atmosphere  was  more  moist  than  now.  This 
follows  from  the  greater  warmth  of  the  climate,  and  the 
greater  extent  and  higher  temperature  of  the  oceans. 
The  land  areas,  although  large,  during  the  times  of  ver- 
dure, compared  with  the  land  areas  of  the  Devonian 
or  Silurian,  were  still  small,  and  the  land  low.  It  must, 
therefore,  have  been  an  era  of  prevailing  clouds  and  mists 
and  abundant  rains.  But  then,  as  now,  there  must  have 
been  inequalities  in  the  distribution  of  rain.  America 
is  now  the  moist  forest  continent  of  the  globe ;  and  the 
great  extent  of  the  coal  fields  of  its  northern  half  suggests 
that  it  may  have  borne  the  same  character  in  the  Carbo- 
niferous age. 

Geography.  — Appalachian  and  Rocky  Mountains  not  yet 
made.  —  On  page  290  it  is  stated  that  the  continents 
in  this  age  were  low,  with  few  mountains.  The  non- 
existence  of  the  Appalachians  of  Pennsylvania  and  Vir- 
ginia is  proved  by  the  fact  that  Carboniferous  rocks 
make  up  a  part  of  the  mass  of  these  mountains  —  partly 
marine  rocks,  indicating  that  the  sea  then  spread  over 
the  region;  partly  coal  beds,  each  bed  evidence  that  a 
great  fresh-water  marsh,  flat  as  all  marshes  are,  for  a 
long  while  occupied  the  region  of  the  present  mountains. 

There  is  the  same  evidence  that  the  mass  of  the  Rocky 
Mountains  had  not  been  lifted  ;  for  marine  Carboniferous 
rocks  constitute  a  large  part  of  these  mountains,  many 
beds  containing  remains  of  the  life  of  the  Carboniferous 
seas  that  covered  that  part  of  North  America.  Only 


314  HISTORICAL   GEOLOGY. 

islands,  or  archipelagoes,  made  by  Arahseah,  and  perhaps 
also  Paleozoic,  ridges,  existed  in  the  midst  of  the  wide- 
spread western  waters. 

Condition  in  the  Subcarloniferous  Period.  —  Through 
the  first  period  of  this  era,  — the  Subcarboniferous,  —  the 
continent  was  almost  as  extensively  beneath  the  sea  as  in 
the  Devonian.  This  is  shown  by  the  nature  and  extent 
of  the  Subcarboniferous  rocks  —  the  great  Crinoidal  Lime- 
stones. 

Transition  to  the  Carboniferous  Period.  —  Finally,  the 
Subcarboniferous  period  closed,  and  the  Carboniferous 
opened.  But,  in  the  transition  from  the  period  of  sub- 
mergence to  that  of  emergence,  required  to  bring  into 
existence  the  great  marshes,  a  widespread  bed  of  pebbles, 
gravel,  and  sand  was  accumulated  by  the  waves  dashing 
rudely  over  the  surface  of  the  rising  continent ;  and  these 
pebble  beds  make  the  Pottsville  Conglomerate,  or  Millstone 
Grit,  that  marks  the  commencement  of  the  Carboniferous 
period  in  a  large  part  of  eastern  North  America,  especially 
along  the  Appalachian  region,  and  also  in  Europe. 

Coal-plant  Areas  in  the  Carboniferous  Period.  —  The 
positions  of  the  great  Coal  areas  of  North  America  (see 
map,  page  235)  are  the  positions,  beyond  question,  of 
the  great  marshes  and  shallow  fresh-water  lakes  of  the 
period.  But  it  is  probable  that  the  number  of  these 
marshes  was  less  than  that  of  the  coal  areas.  The  Appa- 
lachian, Illinois-Indiana,  and  Iowa-Texas  fields  may  have 
made  one  vast  Interior  Continental  marsh  region,  and  those 
of  Rhode  Island,  Nova  Scotia,  and  New  Brunswick  an 
Atlantic  Border  marsh  region,  connected  over  Massachu- 
setts Bay  and  the  Bay  of  Fundy.  It  may  be,  however, 
that  a  low  area  of  dry  land  extending  from  the  region  of 
Cincinnati  southward  across  Kentucky  nearly  or  quite  sepa- 
rated the  Eastern  Interior,  from  the  Central  Interior,  marsh. 

The  Michigan  marsh  region  appears  also  to  have  had  its 
dry  margins,  instead  of  coalescing  with  the  Illinois-Indiana 
or  the  Appalachian  area. 


CARBONIFEROUS   ERA.  315 

It  is  not  to  be  inferred  that  the  marshes  alone  were  cov- 
ered with  verdure.  The  vegetation  probably  spread  over 
all  the  dry  land,  though  making  thick  deposits  of  vege- 
table remains  only  where  there  were  marshes  under  dense 
jungles  and  shallow  lakes  with  their  floating  islands. 

Alternations  of  Condition;  Changes  of  Level.  —  It  has 
been  remarked  that  the  many  alternations  of  the  coal  beds 
with  sandstones,  shales,  conglomerates,  and  limestones 
(page  311),  are  evidence  of  as  many  alternations  of  level, 
or  at  least  alternations  of  condition,  during  the  era.  After 
the  great  marshes  of  the  Continental  Interior  had  been 
long  under  verdure,  the  salt  waters  began  again  to  en- 
croach upon  them  in  consequence  of  a  sinking  of  the  land, 
and  finally  swept  over  the  whole  surface,  destroying  the 
terrestrial  and  fresh-water  life  of  the  area,  but  distrib- 
uting at  the  same  time  the  new  life  of  the  salt  waters. 
Then,  after  another  long  period,  one  perhaps  of  many 
oscillations  in  the  water  level,  in  which  sedimentary  beds 
in  many  alternations  were  formed,  the  continent  again  rose 
to  aerial  life,  and  the  marshes  and  shallow  lakes  were  lux- 
uriant anew  with  the  Carboniferous  vegetation.  Thus  the 
sea  prevailed  at  intervals  —  intervals  of  long  duration  — 
through  the  era  even  of  the  Coal  Measures  ;  for  the  asso- 
ciated sedimentary  beds,  as  has  been  stated,  are  in  most 
localities  at  least  fifty  times  as  thick  as  the  coal  beds.  In 
the  Nova  Scotia  Coal  area,  the  waters  which  came  in  over 
the  coal  beds  were  the  brackish  or  fresh  waters  of  a  great 
estuary  —  that  at  the  mouth  of  the  St.  Lawrence  River  of 
the  Carboniferous  period. 

These  oscillations  continued  until  nearly  3000  feet  of 
strata  were  formed  in  some  parts  of  Pennsylvania,  and 
about  5000  in  Nova  Scotia. 

The  Carboniferous  period  was,  therefore,  ever  varying 
in  its  geography.  A  map  of  its  condition  when  the  great 
coal  beds  were  accumulating  would  have  its  eastern  coast 
line,' from  the  Carolinas  northward,  even  outside  of  the 
present.  The  southern  coast  line  would  pass  through 


316  HISTORICAL  GEOLOGY. 

South  Carolina,  Georgia,  Alabama,  and  northern  Missis- 
sippi, then  turn  northward  around  the  bay  which  occupied 
the  lower  Mississippi  Valley,  then  southward  around  the 
southern  end  of  the  Carboniferous  area  in  Texas ;  thence 
the  coast  line  would  stretch  northward,  bounding  a  sea 
covering  a  large  part  of  the  Rocky  Mountain  region,  for 
the  Coal  period  was,  in  that  part  of  the  continent,  mainly 
a  time  of  limestone-making.  On  the  contrary,  in  a  map 
representing  the  continent  during  the  succeeding  times  of 
submergence,  the  coast  line  would  be  nearly  as  laid  down 
in  the  map,  Fig.  303,  page  287.  Through  these  condi- 
tions, as  the  extremes,  the  continent  may  have  passed 
several  times  in  the  course  of  the  Carboniferous  period. 
Many  of  the  oscillations,  however,  may  have  affected  only 
parts  of  the  continent,  some  parts  of  the  Carboniferous 
area  being  submerged  while  other  parts  were  clothed  with 
vegetation. 

Condition  in  the  Permian  Period.  —  Finally,  in  the 
Permian  period,  the  continent  seems  in  some  degree  to 
have  reverted  to  a  condition  of  submergence  like  that 
of  the  Subcarboniferous,  the  coal  beds  being  insignificant. 

GENERAL  OBSERVATIONS  ON  THE  PALEOZOIC. 

Rocks.  —  1.  Maximum  Thickness.  —  The  maximum 
thickness  of  the  rocks  of  the  various  Paleozoic  eras  in 
North  America  is  approximately  estimated  as  follows  :  — 
Cambrian,  20,000  feet ;  Lower  Silurian,  18,000 ;  Upper 
Silurian,  7000 ;  Devonian,  14,000  ;  Carboniferous,  16,000. 

2.  Diversities  of  the  Different  Continental  Regions  as  to 
Kinds  of  Hocks.  — The  Paleozoic  rocks  of  the  Appalachian 
region  are  mainly  sandstones,  shales,  and  conglomerates  ; 
only  about  one  fourth  of  the  whole  thickness  consists  of 
limestone.  The  rocks  of  the  Central  Interior  are  mostly 
limestone,  fully  two  thirds  being  of  this  nature. 

In  the  Central  Interior,  the  Cambrian  rocks  are  largely 
limestones ;  those  of  the  Lower  Silurian,  even  those  of 


PALEOZOIC   TIME.  317 

the  Hudson  epoch,  are  mostly  limestones  ;  the  Upper 
Silurian  and  Devonian  are  represented  by  an  almost  con- 
tinuous series  of  limestones,  excepting  the  Upper  Devo- 
nian, which  is  represented  by  the  "  Black  Shale "  ;  the 
Subcarboniferous  consists  mostly  of  limestone ;  and  the 
Coal  Measures  include  a  much  larger  proportion  of  lime- 
stone than  in  the  Appalachian  region. 

3.  Diversities  of  the  Appalachian  and  Central  Interior 
Regions  as  to  the  Thickness  of  the  Rocks.  —  In  the  Appala- 
chian region  the  maximum  thickness  of  the  Paleozoic  rocks 
is  more  than  40,000  feet.  But  this  thickness  is  not  observed 
at  any  one  locality,  being  obtained  by  adding  together  the 
greatest  thicknesses  of  the  several  formations  wherever 
observed.  The  greatest  actual  thickness  in  Pennsylvania 
is  about  30,000  feet,  or  nearly  six  miles. 

In  the  central  portions  of  the  Interior  region  the  thick- 
ness varies  from  3000  to  6000  feet ;  and  it  is,  therefore, 
from  one  sixth  to  one  tenth  that  in  the  Appalachian  region. 

Time  Ratios.  —  Judging  from  the  maximum  thick- 
ness of  the  rocks  of  the  several  Paleozoic  ages  in  North 
America,  and  assuming  that  five  feet  of  fragmental  rocks 
may  accumulate  in  the  time  required  for  one  foot  of  lime- 
stone, the  relative  lengths  of  the  Eopaleozoic,  Upper 
Silurian,  Devonian,  and  Carboniferous  ages  were  not  far 
from  6:1:2:2. 

The  method  of  computation  is,  however,  essentially 
uncertain,  since  thickness  of  sediment  must  depend  on 
amount  of  subsidence.  In  a  locality  which  was  not  sub- 
siding, thick  sediments  could  not  accumulate,  even  in 
infinite  time.  But  the  estimates  are  so  far  reliable  as 
to  show  clearly  that  time  moved  on  slowly  in  the  earth's 
first  beginnings. 

Geography. —  Close  of  Archcean  Time. — The  map  on  page 
237  shows  approximately  the  outline  of  the  dry  land  of 
North  America  at  the  close  of  the  Archsean.  The  only 
mountains  were  Archaean  mountains,  among  the  chief  of 
which  were  the  Laureutian  Mountains  of  Canada,  the  Adi- 


318  HISTORICAL  GEOLOGY. 

rondacks  of  northern  New  York,  the  Highlands  of  south- 
eastern New  York  and  New  Jersey,  the  long  Archaean 
range  whose  degraded  remnant  is  seen  in  the  "  Pied- 
mont belt"  of  the  South  Atlantic  states,  and  the  still 
longer  range  which  forms  the  "  backbone  "  of  the  Rocky 
Mountains.  We  cannot  judge  of  the  height  of  these  moun- 
tains then  from  what  we  now  see,  after  all  the  ages  of 
Geology  have  passed  over  them,  for  the  atmosphere  and 
water  have  never  ceased  action  since  the  time  of  their 
uplift,  and  the  amount  of  loss  by  degradation  must  have 
been  very  great ;  while,  on  the  other  hand,  the  altitude  of 
Archaean  ranges  in  the  Appalachian  and  Rocky  Mountain 
regions  may  have  been  increased  by  orogenic  movements 
of  those  regions  in  later  time. 

General  Progress  through  Paleozoic  Time.  —  The  in- 
crease of  dry  land  during  the  Paleozoic  has  been  shown 
(pages  272,  287)  to  have  taken  place  mainly  along  the 
borders  of  the  Archaean,  so  that  the  original  area  was  thus 
gradually  extending.  This  increase  is  well  marked  from 
north  to  south  across  New  York.  At  the  close  of  the  Lower 
Silurian  the  shore  line  was  not  far  from  the  present  position 
of  the  Mohawk,  indicating  but  a  slight  extension  of  the  dry 
land  in  the  course  of  this  very  long  era ;  when  the  Upper 
Silurian  ended,  the  shore  line  was  probably  about  a  score 
of  miles  south  of  the  Mohawk.  When  the  Devonian 
ended  and  the  Carboniferous  age  was  about  opening, 
the  coast  line  was  just  north  of  the  Pennsylvania  boun- 
dary. The  progress  southward  went  on  in  like  manner 
in  Wisconsin,  where  there  is  an  isolated  Archaean  region 
like  that  of  northern  New  York.  By  the  close  of  the 
Lower  Silurian,  the  great  Cincinnati  island  had  emerged ; 
and,  by  the  close  of  the  Devonian,  that  island  had  become 
a  peninsula  connecting  with  the  mainland  in  the  region 
of  northern  Illinois.  (See  map,  Fig.  303,  page  287.) 
The  region  of  the  southern  peninsula  of  Michigan  con- 
tinued through  the  Subcarboniferous  and  the  times  of 
submergence  in  the  Carboniferous  to  be  the  head  of  the 


PALEOZOIC   TIME.  319 

great  Eastern  Interior  bay  of  the  Continental  sea.  In 
the  times  of  emergence,  the  Michigan  bay  became  a  marsh 
or  fresh-water  lake,  filled  with  Coal-measure  vegetation  ; 
and,  at  the  same  times,  as  explained  on  page  315,  the 
continent  east  of  the  western  meridian  of  Missouri  had 
nearly  its  present  extent,  though  not  its  mountains  nor  its 
rivers. 

Regions  of  Rock-making  and  their  Differences.  —  During 
most  of  Paleozoic  time,  the  greater  part  of  the  conti- 
nent was  submerged  beneath  marine  waters,  and  that  part 
was  the  scene  of  nearly  all  the  rock-making.  Areas  of 
fresh  water,  however,  existed  at  times,  especially  in  the 
Devonian  and  Carboniferous,  as  is  proved  by  the  coal 
beds,  and  by  occasional  fresh- water  shells  in  shales  and 
sandstones. 

After  the  emergence  of  the  Cincinnati  and  Tennessee 
islands,  at  the  close  of  the  Lower  Silurian,  the  Interior 
Continental  sea  (as  explained  on  page  263)  was  divided 
into  a  Central  Interior  sea  and  an  Eastern  Interior  sea  or 
bay.  The  eastern  part  of  the  latter  occupied  the  region 
of  the  Appalachian  geosyncline. 

The  Central  Interior  region  afforded  the  conditions  fitted 
for  the  growth  of  Corals  and  Crinoids  and  other  clear- 
water  species,  and  hence  for  the  making  of  limestones  out 
of  their  remains;  for  limestones  are  the  principal  rocks  of 
the  interior.  Yet  there  were  oscillations  in  the  level;  for 
there  are  abrupt  transitions  in  the  limestones,  and  some 
sandstones  and  shales  alternate  with  them.  But  these 
oscillations  were  not  great,  the  whole  thickness  of  the 
rocks,  as  stated  on  page  317,  being  small. 

The  Appalachian  region,  on  the  contrary,  presented  the 
conditions  required  for  fragmental  deposits.  It  was  ap- 
parently a  region  of  immense  sand  reefs  and  mud  flats, 
with  bays,  estuaries,  and  extensive  submerged  offshore 
plateaus.  Here  the  change  of  level  was  very  great;  for 
within  this  region  occur  nearly  six  miles  of  Paleozoic 
formations  (page  317).  This  vast  thickness  indicates  that, 


320  HISTORICAL  GEOLOGY. 

while  there  were  various  upward  and  downward  move- 
ments over  this  Appalachian  region  through  Paleozoic 
time,  the  downward  movements  exceeded  the  upward  even 
by  the  amount  just  stated. 

Mountains  of  Paleozoic  Origin.  —  The  formation  of  the 
Taconic  system  of  mountains  (page  261),  and  the  emer- 
gence of  the  Atlantic  Border  region  from  southern  New 
England  to  Georgia  (page  262),  are  the  most  marked 
geographical  changes  Avhich  occurred  during  Paleozoic 
time.  The  Taconic  range  itself  extends  along  the  north- 
western and  western  boundary  of  New  England,  from 
Canada  to  northwestern  Connecticut.  But  it  was  ap- 
parently only  one  of  a  system  of  approximately  parallel 
contemporaneous  ranges  extending  southwestward  to  Vir- 
ginia and  perhaps  still  farther.  As  in  the  case  of  the 
still  earlier  Archaean  ranges,  the  original  altitude  of  these 
ranges  of  the  Taconic  system  is  matter  for  mere  conjec- 
ture. They  have  suffered  ages  of  erosion,  but  they  may 
have  been  re-elevated  in  later  orogenic  movements.  The 
region  of  western  New  England  and  eastern  New  York 
was  not  so  much  elevated  at  the  time  of  the  Taconic 
movements,  as  to  prevent  the  deposit  of  marine  strata  in 
part  of  the  Hudson  Valley  in  the  Upper  Silurian,  and  in 
the  Connecticut  Valley  even  in  the  Devonian. 

Near  Gaspe  in  eastern  Canada,  and  in  Maine,  New 
Brunswick,  and  Nova  Scotia,  the  unconformability  be- 
tween the  Devonian  and  the  Carboniferous  indicates  some 
mountain-making  movements  at  the  close  of  the  Devonian. 

Rivers ;  Lakes.  —  The  depression  between  the  New 
York  and  the  Canada  Archaean,  dating  from  Archaean 
time,  was  the  first  indication  of  a  future  St.  Lawrence 
channel.  It  continued  to  be  an  arm  of  the  sea,  or  deep 
bay,  through  the  Lower  Silurian,  and  underwent  a  great 
amount  of  subsidence  as  it  received  the  thick  formations 
of  that  era.  After  the  Lower  Silurian  era,  marine  strata 
ceased  to  form,  indicating  thereby  that  the  sea  had  retired  ; 
and  fresh  waters,  derived  from  the  Archaean  heights  of 


PALEOZOIC  TIME.  321 

Canada  and  New  York,  probably  began  their  flow  along 
its  upper  portion,  and  emptied  into  the  St.  Lawrence  Gulf 
of  the  time  not  far  below  Montreal. 

The  Hudson-Champlain  Valley  apparently  dates  from 
Archtean  time,  and  was  a  salt-water  channel  in  the  Lower 
Silurian.  At  the  close  of  the  Lower  Silurian  the  channel 
was  closed  by  the  elevation  of  the  region,  but  it  was 
probably  temporarily  reopened  in  the  Lower  Helderberg 
period.  The  Hudson  River  must  have  commenced  at  the 
close  of  the  Lower  Silurian,  as  an  insignificant  stream, 
draining  a  part  of  the  Adirondacks,  and  emptying  into 
the  Eastern  Interior  sea  near  Albany. 

An  embryo  Mississippi  River  probably  began  early  in 
Paleozoic  time  to  drain  the  Archsean  regions  of  Wisconsin 
and  Minnesota.  But  the  main  part  of  the  Mississippi 
and  its  tributaries,  east  and  west,  was  not  in  existence  in 
the  Paleozoic  ages.  In  the  times  of  Carboniferous  ver- 
dure, when  the  continent  was  in  large  part  above  the  sea 
level,  the  Ohio  and  Mississippi  basins  were  regions  of 
great  marshes,  lakes,  and  bayous,  and  not  of  great  rivers; 
for  great  rivers  could  not  exist  without  high  land  to  sup- 
ply water  and  give  it  a  flow. 

Climate.  —  No  evidence  has  been  found  through  the 
Paleozoic  records  of  any  marked  difference  of  temperature 
between  the  zones.  In  the  Carboniferous  era  the  Arctic 
seas  had  their  Corals  and  Brachiopods,  and  the  Arctic 
lands  their  forests  and  marshes  under  dense  foliage,  no 
less  than  those  of  America  and  Europe.  The  facts  bear- 
ing on  this  subject  are  stated  on  page  312. 

Life.  —  Appearance  and  Disappearance  of  Species.  — 
With  the  beginning  of  each  formation  in  the  series, 
new  species  appeared,  and  the  old  ones  more  or  less  com- 
pletely disappeared.  Local  changes  in  the  life  occurred  in 
connection  even  with  the  minor  transitions  in  the  rock 
formations,  as  in  the  transition  from  a  bed  of  shale  to 
sandstone  or  to  limestone,  and  the  reverse.  Thus,  through 
the  ages,  life  and  death  were  in  concurrent  progress, 


322 


HISTORICAL   GEOLOGY. 


Beginning  and  Ending  of  G-enera,  Families,  and  Higher 
Groups.  —  The  following  table  of  the  range  of  genera 
of  Trilobites  illustrates  the  progress  which  took  place  in 
this  group,  and  exemplifies  the  general  fact  with  regard 
to  other  groups  :  — 


Trilobites  
Olenellus  

Paradoxides.  
Agnostus.  . 

Cambrian 

Lower 
Silurian 

Upper 
Silurian 

Devonia.n 

Carbon- 
iferous 

L. 

M. 

U. 

C. 

T. 

jr. 

0 

I..H. 

L. 

M. 

U. 

B. 

C. 

P. 

ll 

4| 

I 

i 

- 
'- 

1 

> 

^ 

J~~^ 

~-: 

-^ 

?•->•-•..'-•- 

2^^ 

* 

^^ 

Bathyurus  
Asaphus  

^^^ 

B» 

Illcenus  

Co^77ie?ie._._.._.___—. 
Lichas.  
Homalonotus  
Phillipsia  . 

^^ 

^^ 

_...) 

^ 

^^ 

n 

\/ttr>r 

*7*s;j77. 

^ 

~ 

^ 

Griffithides.  

c~ 

^^^= 

In  the  above  table,  the  vertical  columns  correspond 
to  the  eras  and  periods.  The  shaded  area  opposite  the 
name  Trilobites  shows  that  the  group  commenced  in  the 
beginning  of  the  Cambrian,  attained  its  chief  development 
in  the  Lower  Silurian,  then  gradually  declined,  but  con- 
tinued till  the  Permian.  Some  genera  are  seen  to  have 
a  very  limited  range  in  time,  as  Olenellus  and  Paradox- 
ides,  confined  respectively  to  the  Lower  and  Middle 
Cambrian ;  while  Agnostus  extends  through  the  Cam- 


PALEOZOIC   TIME.  323 

brian  and  Lower  Silurian,  and  Homalonotus  through  the 
Silurian  and  a  large  part  of  the  Devonian. 

In  a  similar  manner  the  genera  and  families  of  Braohio- 
pods  began  at  different  periods  or  epochs,  and  continued 
on  for  a  time,  to  become,  in  general,  extinct.  Many 
genera  ended  in  the  course  of  the  Paleozoic  or  at  its 
close ;  only  a  few  continued  into  later  periods.  The 
history  of  other  groups  illustrates  the  same  law. 

Special  Peculiarities  of  Paleozoic  Life.  —  The  following 
facts  show  in  what  respects  the  life  of  the  Paleozoic 
ages  was  peculiarly  ancient:  — 

1.  Not  only  are  the  species  all  extinct  (with  the  pos- 
sible exception  of  a  few  Diatoms  of  the  Carboniferous,  said 
to  be  identical  with  living  species),  but   also  the  great 
majority  of  the  genera. 

2.  Among  Coelenterates,  the  Anthozoans  were  largely 
of  the  tribe  of   Cyathophylloid  corals,  which  is  almost 
exclusively  ancient  or  Paleozoic. 

3.  The  Echinoderms  were  mostly  Crinoids,  and  these 
were  in  great  profusion.     Crinoids  were  far  less  abundant, 
and  of  different  genera,  in  the  Mesozoic;  and  now  very 
few  species  exist. 

4.  Among  Molluscoids,  Brachiopods  were  exceedingly 
abundant :  their  fossil  shells  far  outweigh  the  fossils  of 
any  other  group.     But  in  the  Mesozoic  they  were  much 
less  numerous ;    and   at    the    present  time  the  group  is 
nearly  extinct. 

5.  Among  Mollusks,  the  Cephalopods  were  represented 
very  largely  by  Orthocerata,    but   few  species  of  which 
existed  in  the  early  Mesozoic,  and  none  afterward. 

6.  Among  Arthropods,  Trilobites  were  the  most  com- 
mon Crustaceans  —  a  group  exclusively  Paleozoic. 

7.  Among    Vertebrates,    the    Paleozoic    Fishes    were 
either  Selachians,  Placoderms,  Ganoids,  or  Dipnoans.     Of 
the  Selachians,  a  large  proportion  were  Cestracionts  —  a 
tribe  common  in  the  Mesozoic,  but  now  nearly  extinct. 
Nearly  all  the  Ganoids  had  vertebra  ted  tails.     Compara- 


324  HISTORICAL   GEOLOGY. 

lively  few  Ganoids  with  vertebrated  tails  lived  after  the 
Paleozoic,  and  the  whole  subclass  is  now  nearly  extinct. 
Of  the  Dipnoans,  only  four  species  now  survive.  The 
Amphibians  all  belonged  to  the  order  of  Stegocephala  — 
a  group  which  became  extinct  early  in  the  Mesozoic. 

8.  Among  terrestrial  Plants,  there  were  Lepidoden- 
drids,  Sigillarids,  Calamites  in  great  profusion,  making, 
with  Conifers  and  Ferns,  the  forests  and  jungles  of  the 
Carboniferous  and  later  Devonian :  no  species  of  Lepido- 
dendron  or  Calamites  is  known  after  the  Paleozoic,  and 
only  a  single  Triassic  species  of  Sigillaria. 

Thus,  the  Paleozoic  or  ancient  aspect  of  the  animal 
life  was  produced  through  the  great  predominance  of 
Brachiopods,  Crinoids,  Cyathophylloid  Corals,  Orthocerata, 
Trilobites,  Placoderms,  vertebrate-tailed  Ganoids,  and  Ste- 
gocephala; and  that  of  the  plants,  through  the  Lepidoden- 
drids,  Sigillarids,  and  Calamites.  In  addition  to  this 
should  be  mentioned  the  absence  of  Angiosperms  among 
Plants;  the  absence  of  Dibranchs  among  Cephalopods, 
Brachyurans  among  Crustaceans,  the  higher  orders  (those 
with  complete  metamorphosis)  among  Insects,1  Teleost 
Fishes,  all  modern  orders  of  Amphibia,  all  orders  of  Rep- 
tiles now  existing  except  the  nearly  extinct  Rhynchoce- 
phala,  and  the  entire  classes  of  Birds  and  Mammals. 

Mesozoic  and  Modern  Types  begun  in  Paleozoic  Time.  — 
The  principal  Mesozoic  type  which  began  in  the  Paleo- 
zoic was  the  Reptilian.  But  besides  these  Reptiles  there 
were  the  first  of  the  Decapod  Crustaceans ;  the  first  of 
the  great  group  of  Ammonites,  the  Goniatites  being  of 
this  group;  the  first  of  Scorpions,  Spiders,  Centipeds, 
and  Hexapod  Insects.  The  type  of  Insects  belongs  emi- 
nently to  modern  time  ;  for  it  probably  has  now  its  fullest 
display. 

Thus,  while  the  Paleozoic  ages  were  progressing,  and 
the  types  peculiar  to  them  were  passing  through  their 

1  With  the  exception  of  some  Insects  which  were  probably  Neuropters, 
and  possibly  a  few  Beetles  (Coleopters), 


APPALACHIAN   REVOLUTION.  825 

time  of  greatest  expansion  in  numbers  and  complexity 
of  structure,  there  were  other  types  introduced  which 
were  to  have  their  culmination  in  a  future  age. 

DISTURBANCES  CLOSING  PALEOZOIC   TIME. 

General  Quiet  of  the  Paleozoic  Ages.  —  The  long  ages 
of  the  Paleozoic  passed  with  few  considerable  disturbances 
of  the  strata  of  eastern  North  America.  There  was, 
indeed,  the  elevation  of  the  Taconic  system  of  mountains 
at  the  close  of  the  Lower  Silurian,  accompanied  by  the 
emergence  of  much  of  the  Atlantic  Border  region ;  and 
again,  at  the  close  of  the  Devonian,  there  were  minor 
disturbances  and  upturnings  in  eastern  New  Brunswick, 
part  of  Nova  Scotia,  and  eastern  Canada.  Besides  these 
changes,  there  was,  through  the  ages,  a  gradual  increase 
in  the  amount  of  dry  land ;  and,  through  all  the  periods, 
over  a  large  part  of  the  continent,  slow  oscillations  were 
in  progress,  varying  the  water  level,  and  thus  occasioning 
alternations  in  the  kinds  and  extent  of  the  deposits. 
But  these  movements  of  the  earth's  crust  were  exceed- 
ingly slow  —  probably  less  than  a  foot  a  century.  There . 
may  have  been  many  occasional  quakings  of  the  earth  — 
perhaps  even  exceeding  the  heaviest  of  modern  earth- 
quakes. There  may  have  been  at  times  sudden  risings  or 
sinkings  of  portions  of  the  continental  crust.  But  the 
condition  of  the  strata  of  the  interior  of  the  continent, 
and  of  the  Appalachian  region  south  of  the  Green  Moun- 
tains, indicates  that  general  quiet  prevailed  through  the 
long  Paleozoic  ages.  In  Europe  there  are  more  frequent 
unconformabilities  in  the  series  of  Paleozoic  rocks,  indi- 
cating that  the  progressive  development  of  that  continent 
was  less  simple  and  uniform  than  that  of  North  America. 
But  even  in  Europe  the  changes  in  the  course  of  Paleozoic 
time  were  much  less  considerable  than  those  near  its  close. 

The  Appalachian  the  Region  of  Greatest  Change  of  Level. 
—  The  region  of  greatest  movement  during  these  ages 


326  HISTORICAL  GEOLOGY. 

was  the  Appalachian.  For  it  has  been  shown  that  the 
oscillations  which  there  took  place  resulted  in  subsidences 
of  one  or  more  thousand  feet  with  nearly  every  period 
of  the  Paleozoic.  In  Pennsylvania  and  Virginia  the  sub- 
sidence continued  through  a  large  part  of  the  Carbonifer- 
ous age,  until  it  amounted  to  about  30,000  feet.  But  this 
sinking  was  quiet  in  its  progress,  as  is  proved  by  the  regu- 
larity in  the  series  of  strata. 

The  thickness  of  the  coal  beds  indicates  that  the  coal- 
plant  marshes  were  long  undisturbed,  and  therefore  that 
long  periods  passed  without  appreciable  movement. 

The  Post-Paleozoic,  or  Appalachian,  Revolution. — This 
long  time  of  comparative  quiet  was  brought  to  a  close  by 
one  of  the  most  strongly  marked  periods  of  comparatively 
rapid  change  in  the  course  of  geological  time.  Mountains 
were  made  in  various  parts  of  the  world,  other  great  geo- 
graphical changes  took  place,  and  the  changes  in  the  life, 
of  the  globe  were  as  strongly  marked  as  those  in  geogra- 
phy. It  was  the  close  of  one  of  the  great  seons  in  the 
world's  history,  and  the  beginning  of  another.  Such  an 
event  is  properly  styled  a  revolution. 

.  The  Appalachian  Range.  —  The  most  striking  geographi- 
cal change  in  eastern  North  America  was  the  elevation 
of  the  Appalachian  range.  As  that  range  has  been  taken 
as  a  type  in  the  exposition  of  the  theory  of  mountain- 
making  (page  211),  it  is  unnecessary  here  to  give  any 
detailed  discussion.  Attention  has  already  been  called  to 
the  progressive  subsidence  of  the  geosyncline,  the  accumu- 
lation of  an  enormous  thickness  of  strata,  the  weakening 
of  the  deeply  buried  sediments  by  the  internal  heat  of  the 
earth,  the  final  yielding  to  the  accumulating  strain,  the 
formation  of  a  series  of  approximately  parallel,  more  or 
less  unsymmetrical,  folds,  varied  in  parts  of  the  range  by 
faults  of  thousands  of  feet.  The  Appalachian  range 
proper  —  a  single  orogenic  individual  —  extends  over  a 
distance  of  1000  miles,  from  New  York  to  Alabama. 

The    Appalachian    System.  —  The    Appalachian    range 


APPALACHIAN   REVOLUTION.  327 

is  only  one  of  the  ranges  made  at  this  time  in  eastern 
North  America.  There  was  another  to  the  east,  the 
Acadian  range,  extending  from  Newfoundland  probably 
to  Narragansett  Bay  in  Rhode  Island  —  a  distance  exceed- 
ing 800  miles  (now  partly  submerged).  In  the  metamor- 
phic  processes  connected  with  the  elevation  of  this  range, 
much  of  the  coal  of  Rhode  Island  actually  passed  beyond 
the  anthracite  stage,  and  was  converted  into  graphite.  A 
third  range  belonging  to  the  Appalachian  system  is  the 
Ouachita  range  in  Arkansas  and  the  Indian  Territory. 
There  is  also  evidence  of  post-Carboniferous  disturbance 
in  the  beds  of  the  Paleozoic  trough  extending  from  Gaspe, 
Canada,  to  Worcester,  Massachusetts.  The  upturning 
and  metamorphism  of  the  Devonian  rocks  in  the  Connec- 
ticut Valley  may  belong  to  the  same  date.  In  western 
North  America,  some  orogenic  movements  in  the  Great 
Basin  are  believed  to  date  from  this  time. 

Disturbances  in  Foreign  Countries.  —  In  the  north  of 
England,  and  also  in  the  region  of  the  South  Wales  Coal 
field,  extensive  disturbances  took  place  between  the  Car- 
boniferous and  the  Permian  period.  Murchison  states 
that  the  close  of  the  Carboniferous  period  was  specially 
marked  by  disturbances  and  uplifts ;  that  it  was  then 
"that  the  coal  strata  and  their  antecedent  formations  were 
very  generally  broken  up,  and  thrown,  by  grand  upheavals, 
into  separate  basins,  which  were  fractured  by  numberless 
powerful  dislocations." 

It  is  noteworthy  that  these  disturbances  in  England 
were  not  precisely  contemporaneous  with  the  Appalachian 
revolution  in  eastern  North  America,  the  latter  occurring 
after  the  Permian.  Devonian  and  Carboniferous  rocks 
were  subject  to  pre-Permian  dislocations  also  over  a  large 
region  of  western  Europe  from  Brittany  to  Bohemia,  and 
from  Ardennes  to  the  Vosges  and  the  Black  Forest.  Car- 
boniferous rocks  are  folded  in  the  Urals,  giving  evidence 
of  orogenic  movements  of  post- Carboniferous  date,  though 
the  backbone  of  the  Urals  is  Archaean.  Some  disturb- 


328 


HISTORICAL  GEOLOGY. 


ance  also  took  place  in  the  Alps  about  the  close  of  Paleo- 
zoic time,  though  the  elevation  of  the  Alps  is  chiefly  due 
to  movements  of  much  later  date. 

North  American  Geography  after  the  Appalachian  Revo- 
lution. —  The  accompanying  map  shows  approximately  the 
condition  of  North  America  after  the  Appalachian  revolu- 
tion. Substantially  the  whole  eastern  half  of  the  continent 

FIG.  339. 


Map  of  North  America  after  the  Appalachian  Revolution. 

had  become  dry  land,  the  shore  of  the  Continental  sea  cor- 
responding roughly  with  the  meridian  of  97°  W.  Since 
no  marine  strata  of  early  Mesozoic  age  are  known  any- 
where along  the  Atlantic  or  the  Gulf  border,  it  is  probable 
that  the  shore  line  was  then  even  outside  of  its  present 
position.  In  the  map,  the  shore  line  is  drawn  where  the 
100-fathom  curve  lies  at  present.  It  is  possible,  however, 
that  borings  through  the  Tertiary  and  Cretaceous  forma- 
tions of  the  Atlantic  and  Gulf  border  may  reveal  the 
existence  of  early  Mesozoic  strata  of  which  no  evidence 


APPALACHIAN   REVOLUTION.  329 

has  yet  been  discovered.  West  of  the  meridian  of  97°, 
the  American  continent  was  represented  only  by  islands 
whose  shore  lines  cannot  be  as  yet  exactly  located. 

Geographical  Changes  in  the  Region  of  the  Indian  Ocean. 
—  The  Permian  flora  of  South  Africa,  India,  and  Australia 
is  so  nearly  identical  as  to  require  the  assumption  of  land 
connection  between  those  regions.  The  hypothesis  has 
been  generally  adopted,  that  a  land  area  of  which  Mada- 
gascar, the  Mascarene,  Seychelle,  and  other  islands  in  the 
Indian  Ocean  are  remnants,  connected  South  Africa  with 
India.  This  hypothetical  area  Suess  has  named  G-ond- 
wdiia-land,  from  the  local  name  of  a  series  of  Permian  and 
Triassic  strata  in  India.  Some  eminent  geologists  suppose 
this  land  area  to  have  extended  across  the  Indian  Ocean 
to  Australia  ;  but  that  extension  is  rendered  improbable  by 
the  great  depth  of  the  Indian  Ocean.  Whatever  connec- 
tion existed  between  Africa  and  Australia  is  better  ex- 
plained by  the  hypothesis  of  a  northward  extension  of  the 
Antarctic  continent.  Such  an  extension  of  Antarctic 
land  may  possibly  account  for  the  glacial  conditions  indi- 
cated by  some  of  the  Permian  conglomerates  in  those 
regions  (page  299).  Gondwana-land,  in  the  more  re- 
stricted sense  of  a  land  area  between  Africa  and  India,  is 
supposed  to  have  persisted  until  the  Tertiary  era,  when  it 
subsided,  leaving  the  islands  in  the  western  part  of  the 
Indian  Ocean  as  its  monuments.  Recent  discoveries  indi- 
cate the  occurrence  of  substantially  the  same  Permian 
flora  in  South  America,  in  southern  Brazil,  and  in  Argen- 
tina. This  fact  also  may  find  explanation  in  the  hypoth- 
esis of  northward  extensions  of  the  Antarctic  Continent. 

Change  of  Fauna  and  Flora. — With  perhaps  the  ex- 
ception of  a  few  Diatoms,  no  Paleozoic  species  is  known  to 
have  survived  into  Mesozoic  and  later  times.  Many  species 
doubtless  were  exterminated.  Others  underwent  variation 
and  adaptation,  so  that  the  remains  of  their  modified  descen- 
dants, when  recognized  in  later  strata,  are  classified  as  dis- 
tinct species.  It  cannot  be  affirmed  that  the  extermination 


330  HISTORICAL  GEOLOGY. 

(or  even  the  change  in  species)  was  universal ;  for  the 
strata  accessible  to  study,  as  they  are  confined  to  portions 
of  the  continental  seas,  testify  only  as  to  changes  and 
destructions  in  those  seas,  and  not  respecting  the  life  exist- 
ing elsewhere.  The  causes  of  so  great  a  change  in  fauna 
and  flora  are  only  imperfectly  understood.  The  gradual 
cooling  of  the  sun,  the  progressive  removal  of  water  and 
carbon  dioxide  from  the  atmosphere,  and  the  climatic 
changes  resulting  directly  and  indirectly  from  geographi- 
cal changes,  must  have  profoundly  affected  the  conditions 
of  life.  Changes  of  land  into  sea  or  of  sea  into  land  must 
have  wrought  great  changes  in  the  life  of  extensive 
regions.  Earthquake  waves  and  other  local  catastrophes 
may  have  wrought  widespread  devastation.  (See  page  458 
for  fuller  discussion  of  causes  of  change  in  fauna  and  flora.) 
And  it  must  be  remembered  that  unconformability  always 
means  the  loss,  for  the  particular  area,  of  the  record  of  an 
interval  in  which  migrations  and  other  biological  changes 
may  have  been  in  progress. 

III.   MESOZOIC  TIME. 

Mesozoic,  or  mediaeval,  time,  in  Geological  history,  is 
appropriately  called  the  REPTILIAN  AGE.  In  the  course 
of  it  the  class  of  Reptiles  passed  its  culmination  —  that  is, 
its  species  increased  in  numbers,  size,  and  diversity  of 
forms,  until  they  vastly  exceeded  in  each  of  these  respects 
the  Reptiles  of  either  earlier  or  later  time.  While  the 
culmination  of  Reptiles  is  the  most  characteristic  feature 
of  the  seon,  it  is  also  noteworthy  as  the  time  of  culmina- 
tion and  incipient  decline  of  Amphibians,  Cephalopods, 
and  Cycads ;  and  of  the  commencement  of  Mammals, 
Birds,  Teleost  Fishes,  and  Angiosperms. 

Area  of  Progress  in  Rock-making.  —  The  area  of  rock- 
making  in  North  America,  during  Mesozoic  time,  was 
somewhat  different  from  what  it  was  in  Paleozoic.  In 
early  Paleozoic  time,  nearly  the  whole  continent,  outside 


MESOZOIC   TIME.  331 

of  the  northern  Archgean  area,  was  receiving  its  successive 
formations.  By  the  close  of  Paleozoic  time,  substantially 
the  whole  continent  east  of  the  meridian  of  97°  had  become 
dry  land,  as  is  shown  by  the  absence  of  marine  strata  of 
later  date.  (See  map,  Fig.  339.)  The  areas  of  progress 
in  Mesozoic  time  were  (1)  the  Atlantic  Border,  (2)  the 
G-ulf  Border,  (3)  the  Western  Interior,  (4)  the  Pacific 
Border,  and  (5)  the  Arctic  Area.  In  the  early  Mesozoic, 
only  estuarine  or  fresh-water  deposits  were  formed  along 
the  Atlantic  Border,  and  no  deposits  now  accessible  along 
the  Gulf  Border ;  but  in  later  Mesozoic  time  a  subsidence 
of  these  border  regions  made  them  once  more  regions  of 
marine  sedimentation. 

In  Europe  no  analogous  change  can  be  distinguished; 
for  the  continent  was,  from  the  first,  an  archipelago,  and  it 
continued  to  bear  this  geographical  character,  though  with 
an  increasing  prevalence  of  dry  land,  until  the  middle  of 
Cenozoic  time.  At  the  beginning  of  Mesozoic  time,  west- 
ern England  stood  as  three  or  four  islands  above  the  sea 
(occupying  approximately  the  area  marked  as  covered  by 
Paleozoic  rocks  on  the  map,  page  295) ;  and  the  area  of 
future  rock-making  was  mainly  confined  to  the  intervals 
between  these  islands  and  to  the  submerged  area  on  the 
east  and  southeast.  It  is  probable  that  this  area  and  a 
portion  of  northeastern  France  were,  geologically,  part  of 
a  large  North  Sea  basin. 

Mesozoic  time  includes  three  eras. 

1.  Tr lassie :  named  from  the  Latin  tria,  three,  in  allu- 
sion to  the  fact  that  the  rocks  of  the  era  in  some  parts  of 
Germany  consist  of  three  separate  groups  of  strata.     This 
is   a   local   subdivision,   not  characterizing   the  rocks  in 
Great  Britain  or  in  most  other  parts  of  Europe. 

2.  Jurassic :    named  from  the  Jura  Mountains,  where 
rocks  of  the  era  occur. 

3.  Cretaceous :  named  from  the  Latin  creta,  chalk,  the 
chalk  beds  of  Great  Britain  and  other  regions  in  Europe 
and  America  .being  included  in  the  Cretaceous  formation. 


332  HISTORICAL  GEOLOGY. 

I.  TRIASSIC  AND  JURASSIC  ERAS. 

ROCKS :  KINDS  AND  DISTRIBUTION. 

In  American  Geology,  it  is  convenient  to  treat  these 
two  eras  together,  since  in  several  regions  of  the  country 
it  is  impossible  with  certainty  to  distinguish  the  respective 
rock  formations  from  each  other. 

In  the  Atlantic  Border  region  these  rocks  occupy  narrow 
troughs  or  basins  parallel  with  the  Appalachian  chain,  fol- 
lowing its  varying  courses.  The  most  northerly  of  these 
areas  extends  along  the  western  border  of  Nova  Scotia. 
A  second  occupies  the  valley  of  the  Connecticut  from 
northern  Massachusetts  to  Middletown,  Connecticut,  and 
extends  thence  southwestward  to  New  Haven  on  Long 
Island  Sound,  having  a  trend  nearly  parallel  with  the 
Green  Mountains  ;  it  has  a  length  of  about  110  miles. 
Another  —  the  longest  —  commences  at  the  north  extrem- 
ity of  the  Palisades,  on  the  west  bank  of  the  Hudson 
River,  stretches  southwestward  through  New  Jersey  and 
Pennsylvania  (here  bending  much  to  the  westward,  like 
the  Appalachians  of  the  state),  and  reaches  far  into  the 
State  of  Virginia.  Another  stretches  —  almost  in  the 
line  of  the  last  —  across  the  southern  boundary  of  Virginia 
into  North  Carolina,  and  another  is  comprised  entirely 
within  the  limits  of  the  latter  state.  The  presence  of 
the  Triassic  beneath  the  later  formations  has  been  detected 
in  a  boring  for  a  well  in  one  locality  in  South  Carolina. 
The  Triassic  areas  are  indicated  on  the  map  on  page  235 
by  an  oblique  lining  in  which  the  lines  run  from  the  left 
above  to  the  right  below. 

The  rocks  are  mainly  sandstones  and  conglomerates,  but 
include  some  considerable  beds  of  shale,  and  in  a  few  places 
impure  limestone.  The  sandstones  are  generally  red  or 
brownish  red.  The  freestone,  or  browristone,  of  Portland, 
near  Middletown  in  Connecticut,  and  of  the  vicinity  of 


TRIASSIC   AND   JURASSIC   ERAS.  333 

Newark  in  New  Jersey,  is  from  this  formation.  The 
pebbles  and  sand  of  the  beds  were  derived  mainly  from 
metamorphic  rocks  alongside  of  the  regions  in  which  they 
lie;  and  from  some  of  the  coarser  layers  large  bowlders 
of  granite,  gneiss,  and  mica  schist  may  be  taken.  The 
strata  overlie  directly,  but  unconformably,  these  meta- 
morphic rocks.  Some  of  the  beds  of  shale  are  black  and 
bituminous;  and  near  Richmond,  Virginia,  and  in  North 
Carolina,  there  are  valuable  beds  of  bituminous  coal. 

The  several  ranges  of  this  sandstone  formation  are  re- 
markable for  the  great  number  of  dikes  and  sheets  of  trap 
intersecting  them.  As  the  trap  (diabase)  is  considerably 
harder  than  the  stratified  rocks,  the  dikes  and  sheets  have 
generally  formed  more  or  less  prominent  ridges  (hills  of 
circumdenudation,  page  133).  Mount  Holyoke  in  Massa- 
chusetts, East  and  West  Rocks  near  New  Haven  in  Con- 
necticut, and  the  Palisades  on  the  Hudson  are  a  few 
examples  of  these  trap  ridges.  Trap  is  an  igneous  rock 
—  one  that  was  ejected  in  a  melted  state  from  a  deep- 
seated  source,  through  fissures  made  by  a  fracturing  of 
the  earth's  crust.  The  proofs  that  the  trap  came  up 
through  the  fissures  in  a  melted  state  are  abundant;  for 
the  adjacent  sandstones  are  often  baked  so  as  to  be  very 
hard,  and  sometimes  filled  with  crystallizations,  as  of  epi- 
dote,  tourmaline,  garnet,  hematite,  etc.,  evidently  due  to 
the  heat. 

Owing  to  the  absence  of  marine  fossils,  it  has  been 
somewhat  uncertain  to  what  part  of  the  Triassic  or  Juras- 
sic era  this  formation  along  the  Atlantic  Border  belongs. 
It  is  sometimes  called  the  Jura-Trias,  and  sometimes  the 
Newark  formation.  The  character  of  the  fossil  plants  and 
Vertebrates  indicates  that  it  is  most  probably  Upper  Tri- 
assic, corresponding  to  the  Keuper  and  Rhsetic  of  Europe. 

The  Jurassic  is  perhaps  represented  on  the  Atlan- 
tic Border  by  the  lower  part  of  the  Potomac  formation 
(page  364). 

In  the  Western  Interior  region  there  is  a  sandstone 


334  HISTORICAL   GEOLOGY. 

formation  in  northern  Texas,  extending  northeastward  to 
the  boundary  of  Kansas,  and  westward  into  New  Mexico, 
containing  much  gypsum  (and  hence  called  the  Gypsif erous 
formation),  but  barren  of  fossils,  except  an  occasional  frag- 
ment or  trunk  of  fossil  wood,  which  is  regarded  as  Triassic. 
Triassic  beds  occupy  extensive  areas  along  the  Colorado 
River  and  its  tributaries,  in  Arizona,  Utah,  and  Colorado. 
Triassic  beds  also  occur  in  the  Black  Hills  of  Dakota,  the 
Wasatch  Mountains  and  the  Sierra  Nevada,  and  in  the 
western  ranges  of  the  Great  Basin.  In  a  large  part  of 
the  beds  referred  -to  the  Triassic,  fossils  are  scanty  or 
wanting. 

Jurassic  rocks  occur  near  the  Black  Hills  of  Dakota,  at 
many  localities  along  the  summit  region  of  the  Rocky 
Mountains,  and  in  the  Sierra  Nevada.  Much  of  the 
Jurassic  rock  is  calcareous,  and  in  many  localities  fossilif- 
erous.  The  Upper  Jurassic  of  Colorado,  Wyoming,  and 
Montana  includes  the  Baptanodon  beds  and  the  overlying 
Atlantosaurus  beds.  The  former  have  afforded  fossils  of 
marine  Invertebrates  and  aquatic  Reptiles;  the  latter  are 
fresh-water  deposits,  and  have  yielded  rich  remains  of 
Reptiles  and  Mammals.  The  Atlantosaurus  beds  may 
possibly  be  of  Lower  Cretaceous  age,  representing  the 
Weald  en  formation  of  England.  The  Jurassic  rocks  of 
the  Sierra  Nevada  have  been  to  a  large  extent  metamor- 
phosed into  crystalline  schists,  whose  quartz  veins  are  the 
repositories  of  the  gold. 

In  Europe,  the  Triassic  rocks  of  eastern  France  and 
Germany,  east  and  west  of  the  Rhine,  consist  of  (1)  a 
thick  sandstone,  predominantly  reddish,  but  very  variable 
in  color,  and  often  mottled  (Eunter  Sandsteiri)-,  (2)  a 
fossilif erous  limestone  (Muschelkalk) ;  (3)  a  formation 
consisting  chiefly  of  reddish  and  mottled  shale  and  sand- 
stone (Keuper).  The  uppermost  beds  of  the  Triassic  con- 
stitute the  Rhcetic  formation,  consisting  of  limestone  and 
shale,  and  containing  in  places  remains  of  a  flora  some- 
what transitional  between  the  Triassic  and  the  Jurassic. 


TRIASSIC   AND  JURASSIC   ERAS.  335 

The  Rhsetic  is  considered  by  some  geologists  the  lowest 
member  of  the  Jurassic.  In  England,  the  Triassic  forma- 
tion (No.  6  on  map,  page  295)  consists  of  reddish  sand- 
stone and  shale;  it  is  mostly  confined  to  a  region  just  east 
of  the  Paleozoic  areas  of  Wales  and  northern  England,  and 
to  an  extension  of  this  region  westward  to  Liverpool  Bay 
(or  over  the  interval  between  those  two  Paleozoic  areas) 
and  up  the  west  coast. 

This  formation,  in  Europe,  contains  in  many  places  beds 
of  salt,  and  is -hence  often  called  the  Saliferous  group.  At 
North wich  in  Cheshire,  England,  there  are  two  beds  of 
rock  salt,  90  to  100  feet  thick;  and  there  are  similar  beds 
at  Vic  and  Dieuze  in  Lorraine,  and  in  Wiirtemberg. 

In  the  eastern  Alps,  the  Triassic  shows  a  very  different 
lithological  character  from  that  which  it  bears  in  other 
regions,  the  Upper,  as  well  as  the  Middle,  Triassic  being 
represented  chiefly  by  great  deposits  of  limestone. 

The  Jurassic  rocks  of  Great  Britain  are  divided  into 
two  principal  groups  :  — 

1.  The  Lias  (No.  7  on  map  of  England,  page  295), 
consisting  of  grayish  compact  limestone  strata. 

2.  The   Oolite  (No.   8  on  map,  page  295),  consisting 
mostly  of  whitish  and  grayish  limestones,  part  of  them 
oolitic  (page  40).     One  stratum,  near  the  middle  of  the 
series,  is  a  coral-reef  limestone,  much  like  the  reef  rock 
of  existing  coral  seas,  though  different  in  species  of  coral. 
Near  the  top  of  the  series  there  are  some  local  beds  of 
fresh-water  or  terrestrial  origin,  in  what  is  called  the  Pur- 
beck  group,  and  one  of  them  on  the  island  of  Portland  is 
named,  significantly,  the  Portland  Dirt  Bed. 

On  the  continent  of  Europe,  the  Jurassic  rocks  are 
generally  divided  into  three  parts  commonly  called  in 
Germany,  respectively,  Lias,  Dogger,  and  Malm. 

The  Solenhofen  lithographic  limestone  is  a  very  fine- 
grained rock  (thereby  adapted  for  lithography),  belong- 
ing near  the  top  of  the  Upper  Jurassic  (Malm),  occurring 
in  the  vicinity  of  Solenhofen  and  Eichstadt  in  Bavaria. 


336 


HISTOBICAX,  GEOLOGY. 


LIFE. 
PLANTS. 


The  vegetation  of  the  Triassic  and  Jurassic  periods 
included  numerous  kinds  of  Ferns,  both  large  and  small, 
Equiseta,  and  Conifers,  and  so  far  resembled  that  of  the 
Carboniferous  age.  But  there  were  no  forests  or  jungles  of 
Lepidodendrids  and  Sigillarids.  Instead  of  these  Carbo- 


FIGS.  340,  341. 
340 


CTCADS  :  Fig.  340,  Cycas  circinalis,  x 


niferous  types,  a  group  of  trees  and  shrubs  sparingly 
represented  in  the  Carboniferous,  that  of  the  Cycads,  was 
eminently  characteristic  of  the  Mesozoic  world.  This 
group  has  now  but  few  living  species,  Cycas  and  Zamia 
being  the  best-known  genera.  The  plants  have  the  aspect 
of  Palms  ;  and  there  was,  therefore,  in  the  Mesozoic  for- 


TRIASSIC   AND  JURASSIC   ERAS. 


387 


FIG.  842. 


ests  a  mingling  of  palmlike  foliage  with  that  of  Conifers 

(Spruce,  Cypress,  and  the  like).     But  the  Cjcads  are  not 

Palms.     They  are  Gymnosperms, 

resembling  the  Conifers  both  in 

the   structure   of  the   wood   and 

in  that  of  the  extremely  simple 

flowers.       The     resemblance    to 

Palms  is  mainly  in  the  cluster  of 

great  leaves  at  the  summit,  and 

the  appearance  of  the  exterior  of 

the  trunk.     Fig.  340  represents, 

much  reduced,  a  modern  Cycas, 

and  Fig.   341  the  leaf   Of   a  living  CYOAD  :  Stump  of  MantelUa  megalo- 

Zamia,  one  twentieth  the  actual 

length.      The  fossil  remains  of  Cycads  are  either  their 

FIGS.  843-34T. 


i:  Fig.  343,  Clathropteris  rectiuscula;  344,  Oligocarpia  robustior  (in  fruit);  845, 
Acrostichites  linnseaefolius.  —  CYOADS  :  Fig.  346,  Podozamites  Emmonsi;  84T,  Ptero- 
phyllum  Eiegeri. 


338  HISTORICAL  GEOLOGY. 

trunks  or  leaves.  A  fossil  species  from  the  Portland  Dirt 
Bed  is  represented  in  Fig.  342.  The  trunks  of  some 
Cycads  have  a  height  of  15  or  20  feet.  In  one  respect 
some  Cycads  resemble  the  Ferns,  —  that  is,  in  the  un- 
folding of  the  young  leaf,  —  the  leaf  being  at  first  rolled 
up  into  a  coil,  and  gradually  unrolling  as  it  expands. 

Fossil  plants  are  common  in  the  coal  regions  of  Rich- 
mond, Virginia,  and  North  Carolina,  and  occur  also  in 
other  localities.  Figs.  343  to  345  represent  a  few  of  the 
Ferns  :  Fig.  343,  a  Clathropteris,  from  Easthampton,  Mas- 
sachusetts; Fig.  344,  an  Oligocarpia,  from  Richmond,  Vir- 
ginia, and  the  Trias  of  Europe  ;  Fig.  345,  an  Acrostichites, 
from  Richmond,  Virginia.  Figs.  346  and  347  are  parts  of 
leaves  of  two  species  of  Cycad,  from  North  Carolina. 
Large  cones  of  Conifers  have  also  been  found.  Several  of 
the  American  plants  are  identical  in  species  with  those 
of  the  European  Triassic,  and  a  few  are  akin  to  European 
Jurassic  forms. 

ANIMALS  —  AMERICAN. 

The  American  beds  of  the  Atlantic  Border  region  are 
remarkable  for  the  absence  of  marine  life  :  all  the  species 
appear  to  be  either  those  of  brackish  water,  or  of  fresh 
water,  or  of  the  land. 

Invertebrates.  —  In  the  beds  of  the  Atlantic  Border, 
Sponges,  Coelenterates,  Echinoderms,  and  Molluscoids  are 
unknown ;  and  the  remains  of  Mollusks  are  of  doubtful 
character.  The  Jurassic  beds  of  the  West  contain  many 
species  of  marine  Invertebrates,  and  the  Triassic  a  few. 

The  shells  of  Ostracoid  Crustaceans  are  common  in  New 
Jersey,  Pennsylvania,  Virginia,  and  North  Carolina,  but 
have  not  yet  been  found  in  New  England.  Fig.  348 
represents  one  of  the  little  shells  of  these  bivalve  species, 
called  Estheria.  It  was  long  supposed  to  be  Molluscan. 
The  Estherise  are  brackish-water  species. 

A  few  remains  of  Insects  have  been  found,  and  probably, 
what  is  more  remarkable,  the  tracks  of  several  species. 


TRIASSIC  AND  JURASSIC   ERAS.  339 

These  tracks  were  made  on  the  soft  mud,  probably  by  the 
larvae  of  the  Insects,  for  many  Insects  pass  their  larval 
state  in  the  water.     Fig.   349  represents  one 
of  these  larvae  found  in  shale  at  Turners  Falls, 
Massachusetts;  it  resembles,  according  to  Dr. 
Le  Conte,  the  larva  of  a  modern  Ephemera, 
or  May-fly.     Figs.  350  and  351  are  the  tracks 
of  Insects.     Professor  Hitchcock  named  nearly  30  species 
of  tracks  supposed  to  be  those  of  Insects  and  Crustaceans. 

Vertebrate  . — There  are  evi- 

FIGS.  849-351.  „ 

350         JT\  351            dences    of    the    existence    of 

\  "\    Fishes,  Amphibians,  Reptiles, 

M        /\  I        Birds,  and  Mammals.      With 

1  I             *  the  appearance  of  the  last  two 

)l  ^     f\  i*    types,  the  subkingdom  of  Ver- 

I  x  X  tebrates  was  finally  represented 

v> '  A      r\  I  \    in  all  its  classes. 

vv>-     '\  1.    Fishes.  —  The       Fishes 
INSECTS  :  Fig.  849,  Mormoiucoides  articu-  found  in  the  American  rocks 

latus ;  350, 351,  tracks  of  Insects.  ,      ,  i         /-^  •  i  j 

include   only   Ganoids   and   a 

few  Dipnoans,  although  Selachian  remains  are  common 
in  Europe.  Fig.  352  represents  one  of  the  Ganoids, 
reduced  one  half.  In  this,  as  in  most  Mesozoic  and 

FIG.  352. 


<y±v 

I 


GANOID  :  Catopterus  gracills,  x  } ;  a,  scale  of  same,  natural  size. 

modern  Ganoids,  the  tail  is  but  slightly  vertebrated,  being 
nearly  homocercal. 

2.    Amphibians,  of  the  order  of  Stegocephala,  or  Laby- 
rinthodonts  (page  307),  appear  to  have  reached   their 


340 


HISTORICAL   GEOLOGY. 


greatest  size  and  numbers  in  the  Triassic  era.  A  foreign 
species  is  mentioned  on  page  351.  Footprints  in  the 
Connecticut  Valley  beds  appear  to  indicate  the  existence 
of  American  species.  Figs.  353,  353  a,  and  354,  354  #, 
represent  tracks  of  two  of  these.  It  is  not,  however,  pos- 
sible in  all  cases  to  distinguish  the  tracks  of  Amphibians 
from  those  of  Reptiles. 

3.  Reptiles.  —  The  most  important  Reptilian  remains 
in  the  American  Triassic  and  Jurassic  belong  to  the 
orders  of  Crocodilians  and  Dinosaurs,  though  most  of  the 


353 


FIGS.  858-356. 


*»,  355a 


356  a 


AMPHIBIANS  :  FIGS.  853,  353  a,  tracks  of  Anisichnus  Deweyanus,  x  £ ;  354,  354  a,  Anisich- 
nus  gracilis,  x  §.  —  REPTILES  :  FIGS.  355,  355  a,  Otozoum  Moodii,  x  ^ ;  356,  356  a, 
Anomcepus  scainbus.  In  each  case  the  tracks  of  the  hind  foot  are  marked  a. 

other  orders  known  from  European  specimens  were  also 
more  or  less  abundantly  represented  in  the  American 
rocks.  The  Dinosaurs  were  so  named  from  the  Greek 
Seiko's,  terrible,  and  craO/so?,  lizard,  some  species  being  of 
gigantic  size  (though  others  were  small  animals,  even 
less  than  two  feet  in  length).  In  eastern  North  America, 
they  are  known  by  the  thousands  of  footprints  left  by 
them  in  the  Connecticut  Valley  and  New  Jersey,  and  a 
few  portions  of  skeletons  from  Connecticut,  Pennsylvania, 
and  North  Carolina ;  and  in  the  West,  by  the  huge  skele- 


TBIASSIC    AND    JUKASSIC    ERAS. 


341 


tons  found  in  the  Rocky  Mountain  region.  Of  the  tracks 
in  the  American  Triassic,  referred  more  or  less  probably 
to  Dinosaurs,  some  belonged  to  animals  completely  bipedal 
in  locomotion,  others  to  animals  more  or  less  quadrupedal; 
in  some  cases  the  animals  appear  to  have  rested  the  fore 
feet  on  the  ground  occasionally,  but  not  at  every  step. 
Figs.  355,  355  a,  and  356,  356  #,  represent  respectively 
the  fore  and  hind  feet  of  two  of  the  species.  In  the 
case  of  the  former  species,  tracks  of  the  small  fore  feet 

FIGS.  857,  858. 


Fig.  857,  track  of  Brontozoum  giganteum,  x  J ;  358,  slab  of  sandstone  with  tracks  of  Kep- 
tiles  and  Amphibians,  x  fa. 

are  but  rarely  found.  Fig.  357  represents  one  of  the 
completely  bipedal  species,  no  tracks  of  the  fore  feet 
of  that  species  being  ever  found.  The  track  represented 
in  Fig.  357  is  actually  eighteen  inches  long,  and  that 
of  Fig.  355  a,  nineteen  inches ;  and  probably  each  of  these 
Dinosaurs  was  over  twenty  feet  in  height  when  standing 
on  his  hind  legs.  Although  some  of  the  bipedal  3-toed 
tracks  are  remarkably  like  those  of  birds,  it  is  probable 
that  they  were  all  those  of  Dinosaurs.  The  biped  march 


342  HISTORICAL   GEOLOGY. 

of  many  of  the  Dinosaurs  is  a  birdlike  characteristic, 
and  it  is  connected  with  a  more  or  less  birdlike  pelvis, 
and  (in  many  species)  with  hollow  limb  bones. 

Fig.   359  represents  the  skeleton  of  one  of  the  Dino- 
saurs of  the  Connecticut  Valley. 

FIG.  359. 


DINOSAUR  :  Anchisaurus  colurus,  x  -fa. 


The  Jurassic  beds  of  Colorado  and  Wyoming  have 
yielded  a  richer  harvest  of  Dinosaurian  remains  than 
any  other  localities  in  the  world.  Some  of  these  Jurassic 
Dinosaurs  are  shown  by  their  teeth  to  have  been  herbivo- 
rous, others  carnivorous.  In  one  group  of  the  herbivorous 
species  (Sauropods),  the  jaws  were  toothed  to  the  extrem- 
ity, the  anterior  limbs  were  nearly  as  long  as  the  posterior, 
the  hind  feet  were  5-toed,  and  the  locomotion  was  com- 


TKIASSIC    AND  JUEASSIC   ERAS. 


343 


pletely  quadrupedal.  Fig.  360  shows  a  species  of  this 
group.  To  this  group  belong  the  most  colossal  land 
animals  that  have  ever  existed.  One  species  (Atlanto- 


FIG.  360. 


DINOSAUR  :  Brontosaurus  excelsus,  x 


saurus  immanis)  was  probably  70  or  80  feet  in  length. 
The  other  group  of  herbivorous  Dinosaurs  (the  Preden- 
tata)  had  the  anterior  part  of  the  jaws  toothless,  and 


FIG.  861. 


DINOSAUR  :  Camptosaurus  dispar,  x 


probably  covered  by  a  horny  bill.  The  pelvis  was  in 
several  respects  strikingly  birdlike.  The  hind  limbs 
were  much  longer  than  the  fore  limbs,  and  in  many 


344 


HISTORICAL  GEOLOGY. 


species  the  locomotion  was  completely  bipedal.  The 
inner  and  the  outer  toe  of  the  hind  foot  were  apt  to 
be  small  or  even  wanting,  so  that  the  foot  was  often  func- 
tionally 3-toed.  These  birdlike  characters  were  most 
perfectly  exhibited  in  the  Ornithopods  (from  o/m?,  bird, 
and  Trow?,  foot).  One  of  this  group  is  represented  in 
Fig.  361.  Another  division  of  the  Predentata,  the  Stego- 
saurs,  resembled  the  Ornithopods  in  many  respects,  but 

FIG.  862. 


DINOSAUR  :  Stegosaurus  ungulatus,  x 


differed  from  them  by  the  presence  of  bony  armor,  which 
in  some  species  was  developed  in  a  most  extraordinary 
degree.  The  name,  from  Greek  (Treya,  to  cover,  <ravpos, 
lizard,  refers  to  this  character.  One  of  these  armored 
species  is  shown  in  Fig.  362.  Beside  these  groups  of 
herbivorous  Dinosaurs,  the  carnivorous  Dinosaurs  (Thero- 
pods),  which  had  been  the  only  Dinosaurs  in  the  Triassic, 
were  abundant  also  in  the  Jurassic.  Their  limbs  were 
in  general  similar  to  those  of  the  Ornithopods  (though 


TRIASSIC    AND   JURASSIC    ERAS.  345 

with  important  differences  in  the  pelvis),  but  their  jaws 
were  toothed  to  the  extremity.  Fig.  359  represents  one 
of  the  Triassic  Theropods. 

4.  Birds.  — A  portion  of  a  skull  supposed  to  be  that  of  a 
Bird  has  been  found  in  the  Atlantosaurus  beds  of  Wyoming. 

5.  Mammals.  —  In  the  North  Carolina  Triassic  have  been 
found  two  jawbones  (one  of  which  is  represented  in  Fig. 
363),  representing  two  small  species  of  Mammals,  perhaps 
Marsupials,  but  more  prob- 
ably Monotremes.    The  for- 

mer  of  these  groups  is  now 
represented  by  the  Opossums 
in  America  and  the  Kanga- 

,  ,\         f  •       MAMMAL  :  iawofDromatheriurn  sylvestre,  x  2. 

roos  and  many  other  forms  in 

Australia.  The  Monotremes  (now  represented  b}r  only 
two  genera  in  Australia  and  the  adjacent  islands)  are  the 
lowest  of  all  Mammals,  being  oviparous,  and  resembling 
Reptiles  in  many  features  of  their  anatomy.  Several  other 
Mammals,  probably  all  Marsupials  and  Monotremes,  have 
been  described  by  Marsh  from  Jurassic  beds  in  Wyoming 
and  Colorado. 

The  facts  prove  that  the  land  population  of  Mesozoic 
America  included  Insects,  Amphibians,  Reptiles,  Birds, 
and  Mammals  ;  and  that  the  forests  which  covered  the 
hills  were  mainly  composed  of  Conifers  and  Cycads. 

ANIMALS  —  FOREIGN. 

The  European  rocks  of  these  periods,  especially  of  the 
Jurassic,  abound  in  marine  fossils,  and  afford  a  good  idea 
of  the  Mesozoic  life  of  the  ocean.  The  remains  of  terres- 
trial life  are  also  of  great  interest,  Mammals  and  an  im- 
mense variety  of  Reptiles  occurring  in  both  the  Triassic 
and  the  Jurassic  beds,  and  Birds  in  the  Jurassic. 

Coelenterates.  —  Corals  are  common  in  some  Jurassic 
strata ;  they  are  related  to  the  modern  types  of  corals, 
and  not  to  the  ancient.  Fig.  364  represents  one  of  the 
Oolitic  species. 


346 


HISTORICAL  GEOLOGY. 


Echinoderms.  —  Crinoids  are  of  many  kinds;  yet  their 
number,  as  compared  with  other  fossils,  is  far  less  than  in 
the  preceding  ages  ;  and  they  are  accompanied  by  various 
new  forms  of  Starfishes  and  Echinoids  (page  69).  Fig. 
365  represents  one  of  the  Triassic  Crinoids,  the  Lily 
Encrinite,  or  Encrinus  liliiformis ;  Fig.  366,  an  Echinoid, 
from  the  Oolite,  stripped  of  its  spines ;  and  Fig.  367,  one 
of  the  spines. 


FIGS.  364-367. 


365 


ANTHOZOAN  :    Fig.  364,   Isastrsea  oblonga.  —  CRINOID  :    Fig.  365,  Encrinus  liliiformis.  — 
ECHINOID  :  Fig.  366,  Cidaris  Blumenbachii  (with  spines  removed) ;  367,  spine  of  same. 

Molluscoids.  —  Brachiopods  are  few  compared  with  their 
number  in  the  Paleozoic.  The  last  species  of  the  Pale- 
ozoic families  Spiriferidce  and  Strophomenidoe  lived  in  the 
early  part  of  the  Jurassic  period.  Fig.  368  represents 
one  of  these  last  of  the  Spirifer  group. 

Mollusks.  —  Lamellibranchs  and  Gastropods  abound 
in  species,  and  under  various  new,  and  many  of  them 
modern,  genera.  Species  of  the  genus  G-ryphcea  were 
common  in  the  Lias  and  later  Mesozoic  rocks ;  they  are 
related  to  the  Oyster,  but  have  the  beak  incurved.  Fig. 
369  represents  a  Liassic  species.  Trigonia  (Fig.  370)  is 
a  characteristic  genus  of  the  Mesozoic  ;  the  name  alludes 


TRIASSIC   AKD   JUEASSIC   ERAS. 


347 


to  the  triangular  form  of  the  shell :  the  species  figured  is 
from  the  Oolite.  The  genus  commenced  in  the  Lias,  and 
still  survives  in  the  Australian  seas. 


FIGS.  368-370. 


370 


BRACHIOPOD  :  Fig.  368,  Spiriferina  Walcotti.  —  LAMELLIBRANCHS  :  Fig.  369,  Gryphsea  in- 
curva ;  370,  Trigonia  clavellata. 

But  the  most  remarkable  and  characteristic  of  all 
Mesozoic  Mollusks  were  the  Cephalopods.  This  class 
passed  its  maximum  as  to  number  and  size  in  the  Meso- 
zoic, and  hundreds  of  species  existed.  The  last  of  the 


FIGS.  371,  372. 


371 


CEPHALOPODS  :  Fig.  371,  Stephanoceras  Humphriesianum  ;  372,  Cosmoceras  Jason. 


348  HISTORICAL   GEOLOGY. 

Paleozoic  type  of  Orthocerata  lived  in  the  Triassic  era. 
In  the  same  era,  species  of  Ammonites,  one  of  the  most 
characteristic  of  Mesozoic  groups,  became  common ;  and 
the  new  order  of  Dibranchs  made  its  first  appearance, 
being  represented  by  genera  of  the  Belemnite  family, 
though  the  genus  Belemnites  did  not  appear  until  the 
Lias. 

The  Ammonites  belonged  to  the  order  of  Tetrabranchs, 
and  had  external  chambered  shells  like  the  Orthocerata, 
Nautili  (Fig.  110,  page  75),  and  Goniatites.  Two  Oolitic 
species  are  represented  in  Figs.  371,  372.  One  of  them 
(Fig.  372)  has  the  side  of  the  aperture  very  much  pro- 
373  longed ;  but  the  outer  margin  of  the  shell, 

whether  prolonged  or  not,  is  seldom  well 
preserved.  The  partitions  (or  septa)  with- 
in the  shells  of  Ammonites  are  bent  back  in 
many  folds  (and  much  plaited  within  each 
fold)  at  their  junction  with  the  shell,  so  as 
to  make  deep  plaited  pockets.  A  front 
view  of  the  outer  septum,  with  the  entrances 
to  its  side  pockets,  is  shown  in  Fig.  373. 
Fig.  416  6,  page  371,  illustrates  the  complex 
ciadis-  form  of  the  junction  of  the  edge  of  the 
septum  with  the  shell  (suture)  in  some 
species  of  Ammonites.  The  suture  is  also  shown  in  Fig. 
419.  The  Paleozoic  Goniatites  belonged  to  the  Ammonite 
group,  but  the  pockets  were  much  more  simple  than  in  the 
typical  Ammonites,  the  flexures  of  the  margins  of  the 
partitions  being  without  plications. 

The  fossil  Belemnite  is  an  internal  shell,  analogous  to 
the  pen  or  bone  (osselet)  of  a  Sepia,  or  Cuttlefish  (see 
Fig.  378).  The  part  of  the  shell  most  commonly  pre- 
served is  a  conical  or  club-shaped  body,  shown  in  Figs. 
375,  376,  solid,  except  at  its  upper  (anterior)  end,  which 
incloses  a  conical  cavity.  This  cavity  is  occupied  by 
a  structure  much  resembling  the  chambered  shell  of 
an  Orthoceras,  whose  upper  (anterior)  extremity  is  ex- 


TRIASSIC    AND   JURASSIC   ERAS. 


340 


panded  on  the  dorsal  side  into  a  thin  plate  shown  in  Fig. 
374.  This  plate  is  so  fragile  that  in  general  it  is  pre- 
served only  in  fragments  or  not  at  all.  The  animal  had 


OEPHALOPODS  :  Fig.  374,  complete  osselet  of  a  Belemnite,  restored ;  375,  Belemnites 
clavatus  ;  376,  Belemnites  paxillosus ;  376  a,  outline  of  section  of  same  near  extrem- 
ity ;  377,  fossil  ink  bag  of  a  Cephalopod  ;  378,  Belemnoteuthis  antiqua,  x  |. 

an  ink  bag  like  the  modern  Sepia.  In  some  allied  genera 
the  ink  bag  was  larger ;  and  the  dried  ink  of  these  fossil 
Cephalopods  has  been  used  in  sketching  pictures  of  them. 
Fig.  377  represents  the  ink  bag  of  a  Jurassic  Cephalopod. 
Fig.  378  is  another  related  Cephalopod,  showing  some- 


350 


HISTORICAL  GEOLOGY. 


thing  of  the  form  of  the  animal,  and  also  the  ink  bag  in 
place. 

Arthropods. — The  Crustaceans  were  represented  by 
species  of  rather  modern  aspect.  Trilobites  were  entirely 
extinct.  Tetradecapods  were  represented  by  species  like 
the  modern  Sow-bugs  (Fig.  379).  Decapods  included 
Macrurans,  represented  by  numerous  species  of  Shrimps 
and  Crawfishes  (Fig.  380  shows  a  Triassic  species) ;  and 
(in  the  Jurassic)  Brachyurans,  or  Crabs.  The  presence  of 
this  highest  suborder  is  a  noteworthy  step  of  progress. 

FIGS.  379-382. 


CEUSTACBANS  :  Fig.  879,  Archfeoniscus  Brodiei ;  880,  Pemphix  Sueurii.  —  INSECTS  :  Fig.  881, 
Libellula  ;  382,  wing  cover  of  Buprestis. 

All  but  one  of  the  important  orders  of  Hexapod  Insects 
were  abundant  in  the  Jurassic.  Even  the  highest  order, 
the  Hymenopters  (Bees,  Ants,  etc.),  was  well  represented. 
Of  the  Lepidopters  (Butterflies,  Moths,  etc.),  only  scanty 
remains  have  been  discovered,  whose  reference  to  the  order 
in  question  is  more  or  less  doubtful.  Fig.  381  is  a  Dragon- 
fly from  Solenhofen;  and  Fig.  382,  the  wing  cover  of  a 
Beetle,  from  the  Stonesfield  Oolite. 

Vertebrates.  —  The  Fishes  were  chiefly  Selachians, 
Ganoids,  and  Dipnoans.  Among  the  Selachians,  the 
ancient  group  of  Cestracionts,  characterized  by  a  pavement 


TRIASSIC    AND    JURASSIC    ERAS. 


351 


FIG.  383. 


of  grinding  teeth  (Figs.  129-131,  page  82),  still  continued, 
and  was  represented  by  numerous  species.  There  were 
also,  in  the  Jurassic,  Sharks  with  sharp-edged  teeth,  like 
most  of  those  inhabiting  modern  seas.  Most  of  the 
Ganoids  were  of  modern  type  in  having  the  tail  nearly 
or  quite  homocercal,  as  shown  in  Fig.  383.  One  genus  of 
Dipnoans,  Ceratodus,  occurring  in  both  the  Triassic  and 
the  Jurassic,  is  still  represented  by  two  living  species 
in  Australia.  The  discovery  and  dissection  of  the 
living  Ceratodus  in  Australia  first  revealed  the  Dip- 
noan  nature  of  the  remarkable  teeth  which  had  long  been 
known  as  Triassic  fossils.  It  thus  became  known  that 
Dipnoans  were  abun- 
dant in  both  Meso- 
zoic  and  later  Pale- 
ozoic time.  Beside 
the  ancient  groups 
of  Selachians,  Ga- 
noids, and  Dipnoans, 
there  were  probably 
in  the  Jurassic,  and 
even  in  the  Triassic, 
representatives  of 
the  modern  Bony 
Fishes,  or  Teleosts.  These,  however,  did  not  become 
abundant  until  the  Cretaceous. 

Amphibians  were  common  in  the  European  Trias,  as  in 
the  American,  and  some  were  of  gigantic  size.  They  all 
belonged  to  the  order  of  Stegocephala,  or  Labyrinthodonts 
—  an  order  which  passed  its  culmination  in  the  Triassic, 
and  probably  became  extinct  at  the  close  of  that  era, 
though  a  single  species  has  been  doubtfully  reported  from 
the  Jurassic. 

One  of  these  Triassic  Labyrinthodonts  had  a  skull  over 
two  feet  long,  of  a  form  shown  in  Fig.  384  ;  its  mouth  was 
set  round  with  teeth  three  inches  long  (Fig.  385).  The 
specimen  here  figured  was  found  in  Wiirtemberg.  It  is 


GANOID  :  Fig.  883,  Dapedius  (restored),  from  the  Lias, 
x  J ;  383  a,  scales  of  same. 


352 


HISTORICAL   GEOLOGY. 


probable  that  some  of  the  animals  whose  tracks  are  so 
common  in  the  Connecticut  Valley  were  of  this  type. 
Fig.  386  is  a  reduced  view  of  handlike  tracks,  supposed 
to  have  been  made  by  a  Labyrinthodont.  The  Am- 
phibians of  the  present  day  are  feeble  and  diminutive 
compared  with  their  Triassic  predecessors. 

The  Triassic,  and,  in  even  greater  degree,  the  Jurassic, 
were  characterized  by  the  immense  development  of  Rep- 
tiles. To  the  two  orders  which  had  appeared  in  the  Per- 
mian—  Rhynchocephala  and  Theromorphs  —  were  added 
in  the  Triassic,  Ichthyosaurs,  Plesiosaurs,  Turtles,  Croco- 


:!S4 


AMPHIBIANS  :   Fig.  384,  skull  of  Mastodonsaurus  giganteus,  x  & ;  385,  tooth  of  same ; 
386,  footprints  of  Chirotherium,  x  &. 

diles,  Dinosaurs,  and  Pterosaurs;  and  before  the  close  of 
the  Jurassic  the  earliest  Lizards  (Lacertilians)  appeared. 
The  Theromorphs  became  extinct  at  the  close  of  the 
Triassic,  but  all  the  other  orders  survived  till  the  close 
of  the  Cretaceous  or  later. 

The  Reptiles  included  species  for  each  of  the  elements 
—  the  water,  the  earth,  the  air. 

The  Swimming  Reptiles  have  been  called  Enaliosaurs 
from  the  Greek  emXto?,  marine,  and  o-avpos,  lizard.  They 
include  the  two  orders  of  Ichthyosaurs  and  Plesiosaurs. 

The  Ichthyosaurs  (Fig.  387)  had  a  short  neck,  a  long 


TRIASSIC    AND   JURASSIC   ERAS. 


353 


and  large  head,  enormous  eyes,  and  thin,  doubly  concave, 
and  therefore  fishlike,  vertebrae.  Their  paddles  were 
somewhat  like  the  flippers  of  a  Whale ;  but  their  great, 
vertically  expanded,  caudal  fin,  and  the  large  dorsal 
fin,  gave  them  an  aspect  more  fishlike  than  that  of 
Whales  or  of  any  other  air-breathing  Vertebrates.  The 
name  is  from  the  Greek  &%0u9,  fish,  and  a-avpo^  lizard. 

FIGS.  387-392. 


REPTILES  :  Fig.  38T,  Ichthyosaurus  quadriscissus ;  388,  head  of  Ichthyosaurus  communis, 
x  &  ;  389,  tooth  of  same,  natural  size ;  390  a,  6,  view  and  section  of  vertebra  of  same  ; 
391,  Plesiosaurus  dolichodeirus,  x  &s 5  392  a,  &,  view  and  section  of  vertebra  of  same. 

Fig.  388  represents  the  head  of  an  Ichthyosaur,  one 
thirtieth  the  natural  size,  showing  the  large  eye  and  the 
numerous  teeth.  Fig.  390  a  is  one  of  the  vertebrse, 
reduced,  and  Fig.  390  6,  a  transverse  section  of  the  same, 
exhibiting  the  fact  that  both  surfaces  are  deeply  concave, 
nearly  as  in  fishes ;  Fig.  389  is  one  of  the  teeth,  natural 
size.  Some  of  the  Ichthyosaurs  were  30  or  40  feet  long. 


354  HISTORICAL    GEOLOGY. 

The  Plesiosaurs,  one  of  which  is  represented,  very  much 
reduced,  in  Fig.  391,  had  generally  a  long,  snakelike  neck, 
a  comparatively  short  body,  and  a  small  head.  Fig.  392  a 
represents  one  of  the  vertebrae,  and  392  b  a  section  of  the 
same ;  it  is  doubly  concave,  but  less  so,  and  much  longer, 
than  in  the  Ichthyosaurs.  Their  limbs  were  paddles,  but 
departed  in  general  much  less  from  the  ordinary  structure 
of  a  Reptilian  foot  than  those  of  the  Ichthyosaurs.  Indeed, 
in  some  of  the  earlier  and  less  specialized  members  of  the 
order,  the  limbs  still  retained  some  adaptation  for  walking. 
Some  species  of  Plesiosaur  were  25  to  30  feet  long.  The 
Pliosaurs,  which  are  included  in  the  order  of  Plesiosaurs, 
though  differing  from  the  typical  genus  Plesiosaurus  in 
having  a  larger  head  and  a  shorter  neck,  were  30  to  40 
feet  long.  Remains  of  more  than  70  species  of  Enaliosaurs 
have  been  found  in  the  Jurassic  rocks. 

Besides  these  swimming  Reptiles,  there  were  numerous 
Crocodiles  lO  to  50  feet  long,  and  Dinosaurs,  the  bulkiest 
and  highest  in  rank  of  all  the  class,  25  to  60  feet  long. 

The  Dinosaurs,  in  Europe,  as  in  America,  included  the 
herbivorous  Sauropods,  Ornithopods,  and  Stegosaurs,  and 
the  carnivorous  Theropods.  Among  the  Sauropods,  a 
species  of  Cetiosaurus  was  40  to  50  feet  long.  One  of  the 
best-known  of  the  Theropods  was  the  Megalosaurus ;  it 
was  a  terrestrial  carnivorous  Reptile  about  30  feet  in 
length.  Strongly  contrasted  in  size  with  the  huge  Megalo- 
saurus,  though  belonging  likewise  to  the  Theropods,  was 
the  graceful,  bird-like  Compsognathus,  not  over  two  feet 
in  length,  from  the  lithographic  limestone  of  Kelheim, 
Bavaria. 

The  Reptiles  adapted  for  the  air  —  that  is,  for  flying  — 
constitute  the  order  Pterosaurs,  so  named  from  the  Greek 
Trre/ooV,  wing,  and  cravpos.  The  most  common  genus  is 
called  Pterodactylus.  The  general  form  of  a  Pterodactyl 
is  shown  in  Fig.  393.  The  bones  of  one  of  the  fingers 
are  greatly  elongated,  for  the  purpose  of  supporting  a  fold 
of  skin,  so  as  to  make  it  serve  (like  an  analogous  arrange- 


TRIASSIC   AND  JURASSIC   ERAS. 


355 


ment  in  Bats)  for  flying.  The  name  Pterodactylus  is  from 
the  Greek  Trrepdv,  wing,  and  Sa/crfXo?,  finger.  The  Juras- 
sic Pterodactyls  were  mostly  small,  and  probably  had  the 
habits  of  Bats  ;  the  largest  was  about  the  size  of  ah  Eagle. 


FIG.  393. 


PTEROSATTE  :  Pterodactylus  spectabilis,  natural  size. 

Other  genera  of  Pterosaurs  differed  from  Pterodactylus  in 
having  long  tails.  A  restoration  of  one  of  these,  showing 
the  wing  membranes  and  the  rudder-like  expansion  of  the 
tail,  is  given  in  Fig.  394.  As  Bats  are  flying  Mammals, 
so  the  Pterosaurs  are  simply  flying  Reptiles,  and  have 


356  HISTORICAL   GEOLOGY. 

little  resemblance  to  Birds  in  structure,  except  that  their 
bones  are  hollow,  and  adapted  in  form  for  the  birdlike 
characteristic  of  flying. 

Besides  the  kinds  of  Reptiles  already  mentioned,  there 
were  Turtles  in  both  the  Triassic  and  the  Jurassic,  and 
Lizards  in  the  Jurassic ;  but,  according  to  present  know- 
ledge, the  world  contained  no  Snakes. 

Coprolites  (or  fossil  excrements)  of  both  Reptiles  and 
Fishes  are  common  in  the  bone  beds.  When  cut  and 
polished,  they  have  a  degree  of  beauty  sufficient  to  give 
them  some  value  in  jewelry. 

FIG.  394. 


PTEROSAUR  :  Ehamphorhynchus  phyllurus,  x  \ . 

Remains  of  Birds  have  been  found  in  the  quarries  of 
Solenhofen  (page  335).  They  have  revealed  the  fact 
that  some  of  the  Mesozoic  Birds  were  reptilian  in  certain 
characters.  The  skeletons  found  (Fig.  395)  show  that 
these  Birds  had  long  reptile-like  tails  consisting  of  many 
vertebra?,  and  claws  on  the  digits  of  the  fore  limb  or 
wing,  like  those  of  the  Pterodactyl  and  Bat,  fitting  them 
evidently  for  clinging.  Moreover,  the  metacarpal  bones 
were  free,  as  in  Reptiles,  while  in  modern  Birds  they  are 
immovably  united.  The  mouth  was  provided  with  teeth. 
But,  while  thus  reptilian  in  some  points  of  structure,  they 
were  actually  Birds,  being  feathered  animals,  and  having 
the  expanse  of  the  wing  made,  not  by  an  expanded  mem- 
brane as  in  the  Pterodactyl,  but  by  long  quill  feathers. 


TRIASSIC   AND   JURASSIC   ERAS. 


357 


The  tail  quills  were  arranged  in  a  row  either  side  of  the 
long  tail. 

Remains  of  Mammals  occur  in  the  Rhsetic  beds  of  Ger- 
many and  England,  in  the  Lower  Oolite  at  Stonesfield, 
England,  and  in  the  Middle  Purbeck  beds  of  the  Upper 


FIG.  395. 


f 


BIRD  :  Archaeopteryx  macrura,  x 


358 


HISTORICAL  GEOLOGY. 


Oolite  (page  335).  About  thirty  species  have  been  made 
out,  more  than  twenty  of  them  from  relics  in  the  Middle 
Purbeck.  The  larger  part,  if  not  all,  are  Marsupials  and 
Monotremes.  Figs.  396,  397  represent  the  jaws  of  two 
species  from  Stonesfield,  twice  the  natural  size. 

The  remarkable  transitional  forms  between  Reptiles  and 
Birds,  as  illustrated  by  the  Ornithopod  Dinosaurs  on  the 
one  hand  and  Archceopteryx  on  the  other,  are  of  course  what 

FIGS.  896,  39T. 


R97 


MAMMALS  :  Fig.  396,  Amphilestes  Broderipi,  x  2 ;  39T,  Phascolotherium  Bucklandi,  x  2. 

would  be  expected  in  accordance  with  the  theory  of  evolu- 
tion. Probably  all  the  Triassic  Mammals  are  Monotremes, 
and  all  the  Jurassic  Mammals  Monotremes  and  Marsupials. 
The  theory  of  evolution  would  require  the  class  of  Mam- 
mals to  commence  with  reptile-like  forms,  such  as  Mono- 
tremes. The  remarkable  mammal-like  peculiarities  of  the 
skulls  of  the  Permian  and  Triassic  Theromorph  Reptiles 
are  very  suggestive  as  to  the  ancestry  of  the  Triassic 
Mammals. 

GENERAL  OBSERVATIONS. 

American  Geography.  —  The  Triassic  sandstones  and 
shales  of  the  Atlantic  Border  region  are  sedimentary 
beds ;  consequently,  the  long,  narrow  tracts  of  country 
in  which  they  were  formed  were  occupied,  at  the  time, 
more  or  less  completely  by  water. 

The  absence  of  marine  fossils  has  been  remarked  upon 
as  proving  that  this  water  was  either  brackish  or  fresh  ^ 


TRIASSIC   AND  JURASSIC   ERAS.  359 

and  hence  the  areas  were  estuaries  or  deep  bays  running 
far  into  the  land. 

There  was  probably  an  abundance  of  marine  life  in  the 
ocean,  if  we  may  judge  from  its  diversity  011  the  other 
side  of  the  Atlantic;  but  the  seacoast  of  the  era  must 
have  been  farther  east  than  at  present,  so  that  any  marine 
deposits  that  were  made  are  now  submerged.  The  present 
sea  border  is  shallow  for  a  distance  of  80  miles  from  the 
New  Jersey  coast,  the  depth  of  water  at  this  distance 
being  but  600  feet.  (See  map,  page  18.) 

The  deposits  contain,  on  many  of  the  layers,  footprints, 
ripple-marks,  raindrop  impressions,  and  other  evidences 
that  they  were  formed  partly  in  shallow  waters,  and 
partly  as  sand  flats,  or  emerging  marshes  and  shores,  over 
which  Reptiles  might  have  walked  or  waded.  If,  then, 
they  are  several  thousands  of  feet  thick,  there  must  have 
been  a  progressive  subsidence  of  the  valleys  in  which  the 
deposits  were  formed.  It  is  hence  apparent  that  oscilla- 
tions of  level,  like  those  that  characterized  the  Appalachian 
region  before  and  during  the  Appalachian  revolution,  were 
in  progress.  Two  effects  of  this  subsidence  occurred : 
(1)  The  sandstone  beds  were  more  or  less  faulted  and 
tilted,  those  of  the  Connecticut  Valley  receiving  a  dip  to 
the  east  or  southeast,  those  of  New  Jersey  and  Penn- 
sylvania to  the  northwest.  (2)  In  the  sinking  of  the 
valley,  an  increasing  strain  was  produced  in  the  earth's 
crystalline  crust  beneath,  which  finally  became  so  great 
that  the  crust  broke,  fissures  opened,  and  liquid  rock 
came  up.1  The  dikes  and  sheets  of  trap  are  this  liquid 
rock  solidified  by  cooling.  The  earth's  crust  along  the 

1  In  the  opinion  of  the  editor,  most  of  the  trap  sheets  of  the  Connecti- 
cut Valley  and  New  Jersey  were  poured  out  as  contemporaneous  sheets 
(page  188)  over  the  underlying  strata,  and  subsequently  covered  by  later 
deposits.  According  to  this  view,  the'  eruption  of  the  trap  took  place 
before  the  tilting  and  faulting  which  occurred  at  the  close  of  the  depo- 
sition. The  trap  masses  of  East  and  West  Rock,  near  New  Haven,  and 
the  great  Palisade  sheet  of  New  Jersey,  are  certainly  intrusive,  but  they 
probably  date  from  about  the  same  time  as  the  contemporaneous  sheets. 


360  HISTORICAL   GEOLOGY. 

Connecticut  Valley  for  more  than  100  miles  was  thus  a 
scene  of  igneous  operations.  All  the  Triassic  areas  from 
Nova  Scotia  to  southern  North  Carolina,  a  distance  of 
1000  miles,  were  similarly  broken  through  and  invaded 
by  trap  ejections. 

The  Rocky  Mountain  region  had  been  mostly  submerged 
during  the  Carboniferous  era,  as  shown  by  the  fact  that 
limestones  were  forming  there  in  the  period  of  the  Coal 
Measures,  and  fossiliferous  sandstones  in  the  Permian. 
The  Triassic  sandstone  there  proves,  by  its  nature,  its 
gypsum  in  many  places,  and  the  paucity  of  its  fossils,  that, 
by  some  change,  the  region  had  become  mostly  an  interior 
shallow  salt  sea,  shut  off  to  a  great  extent  from  the  ocean. 
Such  a  sea  would  be  liable  at  times  to  become  too  salt  for 
almost  any  life.  Hence  the  scarcity  or  absence  of  fossils 
in  many  of  the  beds.  The  salt  waters  by  evaporation 
would  have  furnished  gypsum  and  salt  to  the  beds,  as 
happens  now  sometimes  from  sea  water.  It  follows,  then, 
from  the  beds  of  the  Atlantic  Border  as  well  as  those 
of  the  Rocky  Mountain  region,  that  the  continent  during 
the  era  of  these  Mesozoic  beds  was  submerged  to  a  less 
extent  than  in  the  greater  part  of  the  Paleozoic  ages  and 
the  following  portion  of  the  Mesozoic.  The  fossiliferous 
Jurassic  beds  overlying  the  western  Triassic  show  that, 
before  the  Jurassic  period  had  closed,  the  sea  had  again 
free  access  over  large  areas,  and  oceanic  life  was  abundant. 

Foreign  Geography.  —  The  nature  of  the  Triassic  beds 
in  Great  Britain  and  the  continent  of  Europe  shows  that 
there  were  large  shallow  interior  seas  also  on  that  side  of 
the  Atlantic.  The  salt  deposits,  the  paucity  of  fossils  in 
most  of  the  strata,  and  the  general  character  of  the  rocks, 
indicate  conditions  such  as  existed  in  New  York  during 
the  formation  of  the  Onondaga  beds  of  the  Upper  Silurian 
(see  page  274),  and  in  the  Rocky  Mountain  region  during 
the  deposition  of  the  Gypsiferous  formation.  The  lime- 
stone that  intervened,  along  the  Rhine,  between  the  two 
formations  of  sandstone  and  shale,  shows  an  interval  of 


TKIASSIC   AND   JURASSIC   ERAS.  361 

more  open  sea ;  yet  the  impurity  of  the  limestone  suggests 
that  the  ocean  had  not  full  sweep  over  the  region.  The 
great  limestone  deposits  of  the  eastern  Alps  bear  witness 
to  a  submergence  of  that  region  beneath  a  clearer  sea. 

The  beds  of  the  Jurassic  era  mostly  afford  evidence,  both 
from  their  constitution  and  from  their  abundant  marine 
life,  that  the  ocean  again  had  free  sway  over  large  portions 
of  the  continental  area.  Its  limits  in  Great  Britain,  how- 
ever, became  more  contracted  as  the  period  passed ;  and 
toward  its  close  fresh-water  beds  were  forming  in  some 
places  that  had  earlier  in  the  period  been  under  salt  water. 

Climate.  —  The  Jurassic  coral  reefs  of  Great  Britain  indi- 
cate that  England  then  lay  within  the  subtropical  oceanic 
zone.  This  zone  now  has,  in  general,  as  its  outer  limit  the 
parallel  of  27°  or  28°  ;  and,  consequently,  its  Jurassic 
limit,  if  including  England,  reached  twice  as  far  toward 
the  pole  as  now.  It  is  possible,  however,  that  the  line 
would  have  run  along  the  British  Channel,  were  it  not  for 
the  Gulf  Stream  of  the  era,  which  carried  the  subtropical 
temperature  northeastward  through  the  British  seas,  as  it 
now  does  to  Bermuda,  in  latitude  32°. 

The  following  are  other  facts  of  similar  import.  In 
Arctic  America,  species  of  shells  allied  to  those  of  Europe 
and  tropical  South  America  occur  in  latitudes  60°  to  77° 
16'  ;  and  one  species  of  Belemnite  and  one  of  Ammonite 
are  said  to  be  identical  with  species  occurring  in  these  two 
remote  and  now  widely  different  regions.  If  not  absolutely 
identical,  the  evidence  from  them  as  to  oceanic  temper- 
ature is  nearly  the  same.  Moreover,  on  Exmouth  Island, 
in  77°  16'  N.,  remains  of  an  Ichthyosaur  have  been  found, 
and  in  76°  22'  N.,  on  Bathurst  Island,  bones  of  other  large 
Jurassic  Reptiles  (Teleosaurs).  It  is  probable,  therefore, 
that  a  warm-temperate  oceanic  zone  covered  the  Arctic  to 
the  parallel  of  78°,  if  not  beyond.  No  large  living  reptiles 
exist  outside  of  the  torrid  and  warm-temperate  zones. 

It  was  believed,  however,  by  Neumayr,  that  certain  dif- 
ferences between  the  Upper  Jurassic  1'auna  of  the  Medi- 


862  HISTORICAL  GEOLOGY. 

terranean  region  and  that  of  northern  Russia  indicate  that 
an  appreciable  difference  of  climate  had  already  become 
established  between  northern  and  southern  Europe.  The 
evidence  is  not  altogether  conclusive. 

DISTUEBANCES  CLOSING  THE  JUEASSIC  EEA. 

After  the  Jurassic  era,  or  near  its  close,  the  lofty  range 
of  the  Sierra  Nevada  on  the  eastern  boundary  of  California 
was  made.  To  the  same  system  belong  apparently  the 
Cascade  Range  and  the  Blue  Mountains  of  Oregon.  Some 
disturbances  took  place  also  in  the  region  of  the  Coast 
Range  of  California  and  Oregon,  though  that  region  ex- 
perienced a  later  movement  of  elevation  at  the  close  of  the 
Miocene.  The  close  of  the  Jurassic  is  probably  also  the 
time  of  making  of  the  West  Humbolt  Range  and  some 
other  ranges  over  the  dry  plateau  between  the  Sierra 
Nevada  and  the  Wasatch  Range.  Triassic  and  Jurassic 
fossils  have  been  found  in  the  rocks  of  the  Sierra  Nevada, 
while  Cretaceous  fossiliferous  beds  lie  unconformably  over 
the  upturned  strata  of  the  mountains  :  the  former  fact 
proves  that  the  mountain-making  occurred  after  the  Ju- 
rassic era;  and  the  latter,  that  it  took  place  before  the 
Cretaceous. 

II.  CRETACEOUS  EEA. 

GENERAL  CHARACTERISTICS. 

The  Cretaceous,  the  closing  era  of  Mesozoic  time,  was 
also,  in  some  respects,  a  transition  era  between  the  Meso- 
zoic and  Cenozoic.  During  its  progress,  as  is  explained 
beyond,  occurred  the  decline,  and,  at  its  close,  the  extinc- 
tion, of  a  large  number  of  the  tribes  of  the  mediaeval  world; 
while,  at  the  same  time,  there  appeared  in  its  course  other 
tribes  eminently  characteristic  of  the  modern  world. 
Among  the  modernizing  features,  the  most  prominent  are 
the  Angiosperms  among  plants,  and  the  Teleosts  among 
Fishes.  Of  the  Teleosts,  indeed,  some  representatives 


CRETACEOUS   ERA.  863 

probably  appeared  in  the  earlier  Mesozoic ;  but  it  is  not 
certain  that  the  supposed  Triassic  and  Jurassic  Teleosts 
were  not  Ganoids.  The  Teleosts  certainly  first  attained  a 
considerable  development  in  the  Cretaceous. 

The  Angiosperms  include  nearly  all  the  fruit  trees  of 
the  world,  and  constitute  by  far  the  larger  part  of  modern 
forests.  The  Conifers  and  Cycads,  wherever  they  now 
occur  near  groves  of  Angiosperms,  exhibit  the  contrast  be- 
tween the  mediseval  foliage  and  that  of  the  present  age. 
The  Teleosts  (page  83)  embrace  nearly  all  modern  Fishes 
excepting  those  of  the  subclass  of  Selachians,  or  Sharks. 
Their  prevalence  was  as  great  a  change  for  the  waters  as 
the  new  tribes  of  plants  for  the  land. 

AMERICAN  GEOGRAPHY :  AREAS  OF  ROCK-MAKING. 

The  accompanying  map,  Fig.  398,  shows  the  areas  in 
North  America  which  were  submerged  beneath  salt  water 
during  the  Cretaceous.  The  vertical  lining  indicates  the 
parts  that  were  submerged  during  the  Lower  Cretaceous  ; 
the  horizontal  lining,  those  that  were  submerged  during 
the  Upper  Cretaceous ;  and  the  cross  lining,  the  areas 
under  water  through  the  whole  period.  The  scale  of  the 
map  is  too  small  for  the  indication  of  the  fresh-water 
Cretaceous  areas. 

As  shown  by  the  map,  rock-making  was  going  on  along 
the  Atlantic  Border,  the  Gulf  Border,  and  the  Pacific 
Border,  as  well  as  over  the  Western  Interior  (including 
the  summit  region  of  the  Rocky  Mountains).  The  Gulf 
Border  may  be  considered  as  constituting  two  areas  of 
rock-making  —  an  eastern  and  a  western,  —  since  the 
deposits  east  of  the  Mississippi  differ  considerably  from 
those  of  Texas  and  Mexico. 

ROCKS :  KINDS  AND  DISTRIBUTION. 

Both  in  America  and  in  Europe  the  Cretaceous  forma- 
tion is  divided  into  two  periods,  —  the  LOWER  CRETA 
CEOUS  and  the  UPPER  CRETACEOUS. 


364  HISTORICAL   GEOLOGY. 

A  comparison  of  the  map  on  this  page  with  that  on  page 
387  will  show  that  the  Cretaceous  deposits  along  the 
Atlantic  and  Gulf  Borders  are  to  a  very  large  extent  con- 
cealed beneath  the  overlying  Tertiary  strata.  In  the 
Western  Interior  and  along  the  Pacific  Border,  they  con- 
stitute the  surface  rocks  over  large  areas. 

FIG.  898. 


North  America  in  the  Cretaceous  era. 

The  Lower  Cretaceous  is  represented  on  the  Atlantic 
Border  by  the  fresh-water  Potomac  formation,  including 
sandstones  and  shales  and  unconsolidated  sands  and  clays, 
not  exceeding  1200  feet  in  thickness,  and  exposed  in  a 
narrow  and  interrupted  belt  from  Nantucket  to  South 
Carolina.1  The  presence  of  a  few  rare  marine  shells  in 

1  It  is  possible  that  the  lowest  part  of  the  Potomac  formation  (James 
River  and  Rappahannock  stages)  belongs  to  the  Jurassic  (see  page  333), 
and  that  the  uppermost  part  (Albirupian,  or  Raritan,  stage)  belongs  to 
the  Upper  Cretaceous. 


CRETACEOUS   ERA.  365 

this  fresh-water  formation  shows  that  the  coast  line  could 
not  have  been  far  off.  In  the  western  Gulf  Border  the 
Lower  Cretaceous  formation  (Comanche  series)  is  mainly 
marine,  and  consists  largely  of  limestone,  a  part  of  which 
is  chalk.  On  the  Rio  Grande  the  formation  attains  a 
thickness  of  5000  feet,  though  it  is  much  less  over  most 
of  the  "region.  Fresh-water  beds  of  the  Lower  Cretaceous, 
consisting  of  sandstones  and  shales,  and  containing  some 
coal,  appear  in  some  parts  of  the  Rocky  Mountain  region. 

The  Upper  Cretaceous  appears  on  the  Atlantic  Border, 
between  the  Tertiary  of  the  coast  and  the  older  rocks  of 
the  interior,  in  a  continuous  area  extending  from  New 
Jersey  into  Virginia,  and  in  isolated  patches  farther  north 
and  south.  The  rocks  are  marine  deposits  about  500  feet  in 
thickness,  consisting  of  greensand  alternating  with  beds  of 
sand  and  clay.  The  greensand  (locally  called  marl)  consists 
of  common  sand  mixed  with  blackish  or  olive-green  grains 
of  glauconite  (a  hydrous  silicate  of  iron,  alumina,  and 
potash)  formed  by  chemical  changes  at  the  bottom  of 
the  sea  within  the  shells  of  Rhizopods.  Along  the  Gulf 
Border  marine  Upper  Cretaceous  deposits  were  formed, 
consisting  largely  of  limestone,  especially  in  the  western 
area,  where  much  of  the  formation  is  chalk. 

The  Upper  Cretaceous  is  immensely  developed  in  the 
Western  Interior  region,  the  aggregate  maximum  thick- 
ness of  the  beds  of  the  different  epochs  being  over  15,000 
feet.  Four  divisions  are  recognized,  corresponding  to 
the  Dakota,  Colorado,  Montana,  and  Laramie  epochs.  Of 
these,  the  first  and  the  last  are  fresh-water  formations, 
the  others  marine.  The  rocks  of  the  Colorado  epoch  are 
largely  limestones,  including  much  chalk.  The  deposits 
of  the  other  epochs  are  mainly  fragmental  materials, 
including  sandstones,  shales,  and  conglomerates,  with 
unconsolidated  sands  and  clays.  The  Upper  Cretaceous 
is  the  great  coal  formation  of  western  North  America, 
coal  beds  occurring  at  various  horizons,  but  especially 
in  the  Laramie.  The  coal  fields  in  Colorado  alone  have  an 


366  HISTORICAL  GEOLOGY. 

area  of  about  18,000  square  miles.  Coal  has  been  worked 
also  in  Utah,  Wyoming,  Montana,  and  New  Mexico,  and 
at  various  localities  in  British  America.  One  bed  at 
Evanston,  Wyoming,  is  said  to  be  26  feet  thick. 

The  Laramie  beds  represent  the  latest  epoch  of  the 
Cretaceous,  and  show  in  their  fossil  flora  a  transition 
to  the  Tertiary.  This  epoch  is  not  represented  On  the 
Pacific  and  the  Eastern  Gulf  Border,  and  probably  not 
on  the  Atlantic  Border,  the  latest  Cretaceous  beds  of 
those  regions  apparently  belonging  to  the  Montana  epoch. 

In  Europe,  as  in  North  America,  the  Cretaceous  forma- 
tion constitutes  the  surface  rocks  in  areas  which  form 
more  or  less  interrupted  borders  of  the  Tertiary  regions, 
or  insular  areas  within  those  regions,  indicating  that  the 
Cretaceous  seas  covered  in  general  the  areas  now  occupied 
by  both  Cretaceous  and  Tertiary  rocks. 

In  England,  the  Cretaceous  formation  occupies  most 
of  the  southeastern  part  of  the  country  (9  and  10,  on  map, 
page  295).  The  Lower  Cretaceous  includes,  as  its  basal 
member,  the  Wealden  formation  (9,  on  map),  which  is 
subdivided  into  the  Hastings  Sand  and  the  Weald  Clay. 
This  is  a  fresh- water  formation  deposited  in  a  great  delta 
20,000  square  miles  in  area.  The  remainder  of  the  Lower 
Cretaceous  and  the  whole  Upper  Cretaceous  consist  of 
marine  deposits,  mostly  greensand  and  chalk.  Some  of 
the  chalk  beds  abound  in  concretions  of  flint,  which 
consist  largely  of  Diatoms,  Sponge  spicules,  and  other 
siliceous  organisms.  The  Cretaceous  formations  of  north- 
ern France,  Belgium,  western  Germany,  and  Denmark 
much  resemble  those  of  England.  Chalk  appears  also 
farther  east,  in  southern  Russia.  In  Saxony  and  Bohe- 
mia the  Cretaceous  rocks  are  mainly  sandstones.  In 
the  Mediterranean  region,  where  there  is  a  great  de- 
velopment of  the  Cretaceous,  the  rocks  are  mostly 
limestones,  but  do  not  include  the  chalk  and  green- 
sand  which  are  so  characteristic  of  the  northern  Cre- 
taceous region. 


CRETACEOUS  ERA. 


367 


LIFE. 

PLANTS. 


The  first  of  Angiosperms,  both  Monocotyledons  and 
Dicotyledons,  as  already  stated,  date  from  the  Cretaceous 
period.  Leaves  of  a  few  American  species  of  Dicoty- 
ledons are  represented  in  Figs.  399-402;  Fig.  401,  a 
species  of  Sassafras;  Figs.  899,  400,  species  of  Lirioden- 


FIGS.  399-402. 


ANGIOSPERMS  :  Fig.  399,  Liriodendron  primaevum  ;  400,  Liriodendron  Meekii ;  401,  Sassafras 
cretaceum ;  402,  Salix  Meekii. 

dron;  Fig.  402,  a  Willow  ;  and  with  these  occur  leaves 
of  Oak,  Dogwood,  Beech,  Poplar,  etc.  Among  the  Mono- 
cotyledons are  the  earliest  of  the  great  family  of  the 
Palms. 

Beside  these  highest  of  plants,  there  were  also  Con- 
ifers, Ferns,  and  Seaweeds,  as  in  former  time,  with  some 


368 


HISTORICAL  GEOLOGY, 


Cycads.  The  microscopic  Algae  called  Diatoms  (page 
88),  which  make  siliceous  shells,  and  others  called  Des- 
mids,  which  consist  of  simple  green  cells  without  any 
skeleton,  were  very  abundant.  Both  occur  fossil  in  flint; 
and  the  Diatoms  are  believed  to  have  contributed  part  of 
the  silica  of  which  the  flint  is  formed. 


ANIMALS. 

Protozoans.  —  The  simplest  of  animals,  Foraminifers, 
were  of  great  geological  importance  in  the  Cretaceous 
period ;  for  the  Chalk  is  supposed  to  be  made  mostly  of 
their  minute  calcareous  shells.  The  powdered  chalk  is 
often  found  to  contain  large  numbers  of  these  shells,  the 
great  majority  of  which  do  not  exceed  a  pin's  head  in 
size.  A  few  of  the  forms  are  represented  in  Figs.  403- 
407,  all  very  much  enlarged,  except  Fig.  407,  which  is 
natural  size.  A  very  common  kind  resembles  Fig.  50 


404 


FIGS.  403-407. 
405  406 


FORAMINIFEBS  :   Fig.  403,  Lituola  nautiloidea;   404,  Flabellina  rugosa;  405,  Chrysalidina 
gradata ;  406,  Cuneolina  pavonia ;  40T,  Patellina  Texana. 

(page  61),  and  is  named  Rotalia.  Fig.  407  represents  a 
large  disk-shaped  species  from  Texas. 

Sponges.  —  Sponges  were  also  very  abundant,  and 
their  siliceous  spicules  (page  63)  were  another  important 
source  of  the  silica  of  the  flints.  The  skeletons  of  some 
of  the  Sponges,  both  of  the  Cretaceous  era  and  of  modern 
time,  in  the  deeper  seas,  consist  wholly  of  silica.  Fig.  408 
represents  a  species  whose  skeleton  was  probably  siliceous. 

Coelenterates.  —  Corals  of  modern  type  are  not  uncom- 
mon fossils. 


CRETACEOUS  ERA. 


369 


FIG.  408. 


Echinoderms.  —  Echinoids  are  abundant ;  and  many  of 
the  Echinoids  are  of  the  highest  division  of  the  class, 
in  which  the  radial  arrangement  of  parts  becomes  largely 
subordinated  to  a  bilateral  sym- 
metry. This  group  commenced 
in  the  previous  era,  but  became 
more  abundant  in  the  Qretaceous. 

Mollusks.  —  Figs.  409-412  rep- 
resent some  of  the  most  charac- 
teristic species  of  Lamellibranchs 
from  the  American  Cretaceous. 
All  these  are  of  genera  now  ex- 
tinct ;  but  many  genera  both  of 
Lamellibranchs  and  Gastropods 
that  still  survive  were  already  in  existence. 

Fig.  413  represents  one  of  the  Rudista,  a  remarkable 
group  of   Lamellibranchs,  peculiar  to  the  Cretaceous,  in 

FIGS.  409-412. 


SPONGE  :  Siphonia  lobata. 


410  N 


LAMELLIBRANCHS:  Fig 


J.  Exogyra  costata ;  410,  Gryphaea  vesicularis  ;    411,  Gryphsea 
Pitcher! ;  412,  Inoceramus  labiatus. 

which  the  two  valves  of  the  shell  are  extremely  unequal, 
the  small  left  valve  appearing  as  a  sort  of  cover  to  the 
deep  conical  right  valve, 


370 


HISTORICAL   GEOLOGY. 


Fio.  413. 


Figs.  414,  415,  represent  two  American  species  of  Gas- 
tropods. 

But  the  Cephalopods,  in  this  era  as  in  the  preceding, 
were  the  most  characteristic  class  of  Mollusks.  The 
Tetrabranchs  were  represented  by  numerous  species  of 
the  Ammonite  group,  and  the  Dibranehs  by  Belemnites. 
Figs.  416-420  are  Cephalopods,  all  American  species  ex- 
cept Fig.  418.  Fig.  416  is  a  front  view 
of  a  species  of  the  Ammonite  group, 
showing  the  pockets  formed  by  the 
crumpling  of  the  edge  of  the  outer  sep- 
tum. Fig.  416  b  shows  the  extremely 
complicated  form  of  the  suture  in  this 
species.  Some  of  the  Jurassic  and  Cre- 
taceous Ammonites  are  3  or  4  feet  in 
diameter.  Especially  characteristic  of 
the  Cretaceous,  though  not  unknown  in 
previous  eras,  were  genera  of  the  Ammo- 
nite group  in  which  the  shell  departed 
from  the  form  of  a  closely  coiled  discoidal 
spiral  (Fig.  371,  page  347)  which  was 
typical  in  the  group.  Three  of  these 
aberrant  forms  are  shown  in  Figs.  417— 
419.  Fig.  417  is  the  loosely  coiled 
Scaphites  ;  Fig.  418,  coiled  in  a  turreted 
spiral,  is  a  Turrilites  (Latin  turris, 
Hip-  tower)  ;  Fig.  419  is  the  straight  Bacu- 

7  .  r        .       ,          7  „„, 

htes  (Latin  oaculum,  staff). 

Fig.  420  represents  a  species  of  Belemnite  common  in 
the  Cretaceous  beds  of  New  Jersey. 

Vertebrates.  —  There  were  great  numbers  of  Teleosts,  or 
Osseous  Fishes,  allied  to  the  Herring,  Salmon,  Mackerel, 
etc.  They  occur  along  with  numerous  Sharks  of  both 
ancient  and  modern  types,  and  also  many  Ganoids.  Thus 
the  ancient  and  modern  forms  of  Fishes  were  associated 
in  the  population  of  the  Cretaceous  seas,  the  latter,  how- 
ever, greatly  predominating,  especially  in  the  latter  part 


purites  Toucasianus. 


CRETACEOUS  ERA. 
FIGS.  414-420. 


371 


416  a 


4166 


417 


GASTROPODS  :  Fig.  414,  Fasciolaria  buccinoides  ;  415,  Pyrifusus  Newberryi.  —  CEPHALOPODS  : 
Fig.  416,  Placenticeras  placenta  ;  416  <?-,  same,  in  profile,  reduced  ;  416  6,  diagram  show- 
ing form  of  suture  in  same ;  417,  Scaphites  larvaeformis  ;  418,  Turrilites  cateuatus  •  419 
Baculites  ovatus  ;  420,  Belemnitella  Americana, 


372 


HISTORICAL   GEOLOGY. 


of  the  era.     Fig.  421  represents  one  of  these  Teleost  Fishes, 
related  to  the  Salmon  and  Smelt. 

Reptiles  included  species  of  all  the  orders  occurring  in 
the  Jurassic.     The  Plesiosaurs  were  represented  by  the 


PIG.  421. 


TELEOST  :  Osmeroides  Lewesiensis,  x  J. 

genera  Cimoliosaurus,  Elasmosaurus,  etc.,  some  species  of 
which  were  50  feet  in  length.  The  Dinosaurs  included 
species  of  all  the  groups  represented  in  the  Jurassic,  though 
the  Sauropods  appear  to  have  become  extinct  before  the 
close  of  the  Cretaceous.  Lcelaps  is  a  well-known  example 

FIG.  422. 


DINOSAUR  :  Triceratops  prorsus,  x 

of  the  Theropods,  and  Iguanodon  and  Hadrosaurus  of  the 
Ornithopods.  Besides  Ornithopods  and  Stegosaurs,  the 
Predentata  were  represented  by  the  remarkable  Horned 
Dinosaurs,  or  Oeratopsidce  (Greek  /ce/oa?,  horn,  cn/rt?,  aspect), 
peculiar  to  the  Laramie  beds  (Fig.  422).  These  resem- 


CKETACEOUS  ERA. 


373 


bled  in  many  respects  the  Stegosaurs,  but  were  strongly 
characterized  by  the  great  horn  cores  shown  in  the  figure, 
which  doubtless  supported  epidermic  horns  like  those  of 
cattle.  Among  the  Pterosaurs,  Pteranodon  differed  from 
the  Jurassic  genera  (and  from  other  Cretaceous  genera) 
in  being  destitute  of  teeth.  Two  species  from  Kansas  had 
a  spread  of  wings  of  20  to  25  feet. 

There  was  also  an  order  of  Reptiles  peculiar  to  the  Cre- 
taceous, that  of  the  Mosasaurs,  or  Pythonomorphs  :  great 

FiGS.  428,  424. 


MOSASATJRS  :  Fig.  423,  Mosasaurus  Camperi,  x 
dispar,  x  £. 


;  424,  lower  jaw  of  Edestosaurus 


snakelike  Reptiles,  15  to  75  feet  long,  swimming  by 
means  of  four  paddles  —  literally  the  Sea  Serpents  of  the 
era.  The  remains  of  the  head  of  one,  from  the  banks  of 
the  river  Meuse  in  Holland  (whence  the  name),  are  repre- 
sented in  Fig.  423.  The  American  rocks  have  afforded 
nearly  fifty  species  of  these  Mosasaurs.  The  head  of  the 
largest  was  four  feet  long,  and  the  mouth  was  of  enormous 
size.  Moreover,  these  Reptiles  had  a  movable  joint  in  the 
lower  jaw,  on  either  side,  in  place  of  the  usual  suture  (at  a, 


374 


HISTOEICAL   GEOLOGY. 


FIG.  425. 


in  Fig.  424),  which  enabled  the  two  rami  of  a  jaw  (since 
the  rami  were  not  united  at  their  extremities)  to  act  like 
a  pair  of  arms,  in  working  down  the  immense  throat  any 
large  animal  they  might  undertake  to  swallow  whole.  A 
tooth  of  one  of  the  Mosasaurs,  half  the  natural  size,  is 
shown  in  Fig.  425. 

Among  the  orders  of  Reptiles  now  living,  there  were 
numerous  species  of  Crocodiles  and  Turtles ;  one  of  the 
latter,  from  Kansas,  measuring  15  feet,  according  to  Cope, 
between  the  tips  of  the  extended  flippers.  There  were 
also  a  few  Lizards,  and  the  earliest  of  Snakes. 

The  Birds  of  the  Cretaceous  were  all  apparently  free 
from  the  reptilian  characters  of  long  tail  and  free  meta- 
carpals,  possessed  by  the  Jurassic  Archce- 
opteryx ;  but  some  of  them,  as  first 
made  known  by  Marsh,  still  retained 
teeth. 

Fig.  426,  from  Marsh,  represents  the 
skeleton  of  Hesperornis  regalis,  one  eighth 
the  natural  size  —  a  large  Bird  with  rudi- 
mentary wings,  flat  sternum  (as  in  the 
Ostriches),  and  teeth  inserted  in  a  groove. 
It  resembled  the  Loons,  or  Divers,  in 
several  features  of  the  skeleton,  and  was 
probably  aquatic  in  habit.  Fig.  432 
represents  a  very  different  Bird,  Ichthy- 
ornis  victor  —  a  Bird  of  moderate  size, 
with  well-developed  wings,  keeled  ster- 
num, teeth  inserted  in  sockets,  but  with 
the  very  remarkable  character  "of  bi- 
concave vertebrae.  Both  these  Birds  are 
from  Kansas,  but  a  Bird  apparently  allied 
to  Ichthyornis  has  been  found  in  the 
Greensarid  of  England.  Apparently  there  were  other  Cre- 
taceous Birds  which  were  toothless,  and  related  to  the 
modern  Cormorants  and  Waders. 

Mammals  are  represented  by  numerous  teeth  and  frag- 


Tooth  of  Mosasaurus 
princeps,  x  £. 


CRETACEOUS   ERA. 

FIGS.  426-481. 


375 


TOOTHED  BIRD  :  Fig.  426,  Hesperornis  regalis,  skeleton,  x 
x  4 ;  429, 430,  vertebrae,  x  J ;  481,  pelvis,  side  view,  x  * 
a,  acetabulum. 


P 

\  ;  427,  lower  jaw,  x  £ ;  428,  tooth, 
;  il,  ilium  ;  is,  ischium ;  p,  pubis ; 


376  HISTORICAL   GEOLOGY. 

ments  of  jaws,  and  a  few  fragments  of  other  bones,  from 
the  Laramie  beds  of  North  America,  and  by  a  single  tooth 
from  the  Wealden  in  England.  They  are  probably  all 
Monotremes  and  Marsupials. 

GENERAL   OBSERVATIONS. 

Geography.  —  The  Cretaceous,  both  in  North  America 
and  in  Europe,  as  compared  with  the  earlier  periods  of  the 
Mesozoic,  was  eminently  a  period  of  submergence.  This 
is  indicated  by  the  large  areas  occupied  by  marine  forma- 
tions ;  and  especially  by  the  large  areas  of  chalk  and  other 
limestones.  The  deposits  of  chalk  must  have  been  formed, 
not  in  shallow  waters  adjacent  to  the  shores,  but  in  open 
seas.  It  is  not  probable,  however,  that  the  seas  in  which 
the  chalk  was  deposited  were  of  oceanic  depth.  Forami- 
nifers  are  animals,  not  of  the  abyssal  depths,  but  of  the 
surface,  the  shells  sinking  to  the  bottom  only  after  the 
death  of  the  animals ;  and  a  f oraminiferal  deposit  is  there- 
fore evidence  of  an  open  sea  comparatively  free  from 
detritus,  but  not  necessarily  of  great  depth.  The  other 
fossils  of  the  chalk  belong  apparently  not  to  the  abyssal 
fauna,  but  to  that  of  comparatively  shallow  water. 

As  shown  for  North  America  by  the  map  on  page  364, 
the  submergence  did  not  attain  its  maximum  until  the 
earlier  part  of  the  Upper  Cretaceous.  The  deposits  of  the 
Lower  Cretaceous  were  largely  of  fresh-water  origin,  on 
both  sides  of  the  Atlantic. 

On  the  Atlantic  Border  of  North  America,  the  strata  of 
the  Upper  Cretaceous  are  the  first  marine  deposits  known 
since  the  Lower  Silurian.  The  geanticlinal  elevation 
formed  at  the  time  of  the  Taconic  Revolution  seems  at 
last  to  have  subsided.  At  the  time  of  the  greatest  sub- 
mergence, Chesapeake  and  Delaware  bays  were  in  the 
ocean ;  Florida  was  under  water ;  the  region  of  the  Mis- 
souri River  was  a  salt-water  region  ;  the  Rocky  Mountain 
region  was  largely  submerged.  This  mountain  region  was 


CRETACEOUS   ERA. 


377 


in  some  parts  at  least  10,000  feet  lower  than  now,  the  Cre- 
taceous beds  having  this  elevation  upon  it.     The  Mexican 


FIG.  432. 


TOOTHED  BIRD  :  Ichthyornis  victor,  x  £. 

Gulf  spread  over  the  Gulf  States  from  Florida  to  Texas, 
and  extended  northward  to  the  mouth  of  the  Ohio  ;  while 
a  vast  mediterranean  sea  stretched  from  the  western  part 


378  HISTORICAL   GEOLOGY. 

of  the  Gulf  of  Mexico,  northward  over  the  great  plains 
and  the  summit  region  of  the  Rocky  Mountains,  probably 
even  to  the  Arctic  Ocean  —  a  distance  of  3000  miles. 
About  the  middle  of  the  Upper  Cretaceous,  there  was  a 
shallowing  of  the  sea  and  an  emergence  of  the  land  far 
north  in  British  America,  so  that  the  great  western  medi- 
terranean was  cut  off  from  the  Arctic  Ocean,  and  became 
a  part  of  the  Gulf  of  Mexico,  though  still  having  a  length 
of  2000  miles  or  more.  Gradually  the  area  of  this  great 
western  gulf  contracted  along  its  eastern  border,  and  the 
depth  diminished;  until  at  last,  in  the  Laramie  epoch, 
brackish  and  fresh  waters  took  the  place  of  the  seas  in 
which  chalk  and  other  limestones  had  been  deposited. 

The  Upper  Cretaceous  (and  especially  the  Laramie 
epoch)  was  the  great  coal  period  of  western  North  Amer- 
ica, as  the  Carboniferous  period  was  the  coal  period  of 
eastern  -North  America  and  western  Europe.  In  each 
case,  a  large  area  which  had  been  submerged  beneath  the 
sea  was  passing  through  an  epoch  of  transition  to  terres- 
trial conditions.  For  a  long  time  the  area  was  balancing 
near  the  sea  level,  now  emerging  and  clothing  itself  with 
luxuriant  vegetation,  now  submerged  and  receiving  sedi- 
mentary deposits.  The  kinds  of  plants  which  made  the 
Cretaceous  forests  were,  however,  widely  different  from 
those  of  the  Carboniferous. 

Climate.  —  Although  there  is  clearer  indication  of  dif- 
ferentiation of  zones  of  climate  in  the  Cretaceous  than  in 
any  earlier  period,  a  warm  climate  still  prevailed  even 
in  high  northern  latitudes.  The  Cycads  of  the  Lower 
Cretaceous  in  Greenland  indicate,  according  to  Heer,  a 
mean  temperature  not  below  70°  F.  There  appear  to  have 
been  no  true  coral  reefs  in  the  British  seas,  though  such 
reefs  were  certainly  present  in  the  Mediterranean  basin. 
The  isotherm  of  68°  for  the  coldest  winter  month  appar- 
ently passed  south,  but  not  far  south,  of  Great  Britain. 
The  plants  of  the  upper  Missouri  region  indicate  a  warm- 
temperate  climate  over  that  territory. 


MESOZOIC  TIME.  379 


GENERAL  OBSERVATIONS  ON  THE  MESOZOIC. 

Time  Ratios.  —  The  ratios  between  the  Eopaleozoic, 
Upper  Silurian,  Devonian,  and  Carboniferous  ages,  as  to 
the  length  of  time  that  elapsed  during  their  progress,  or 
their  time  ratios,  are  stated  on  page  317  as  probably  not  far 
from  6:1:2:2.  By  the  same  method,  it  follows  that 
the  ratio  for  the  time  of  the  Paleozoic  and  Mesozoic  was 
nearly  4:1.  That  is,  Mesozoic  time  was  about  one  fourth 
as  long  as  the  Paleozoic  ;  and  the  three  eras  of  the  Mesozoic 
were  not  far  from  equal,  the  Cretaceous  being  probably 
somewhat  the  longest. 

American  Geography.  — On  page  331  it  is  remarked 
that  the  Mesozoic  formations  were  confined  to  the  Atlantic, 
Pacific,  and  Gulf  Border  regions,  the  Arctic  region,  and 
an  Interior  region  west  of  the  Mississippi  covering  much 
of  the  Rocky  Mountain  area ;  and  that  the  portion  of  the 
continent  between  that  Interior  region  and  the  Atlantic 
Border  had  probably  become  part  of  the  dry  land.  The 
facts  which  have  been  presented  in  the  preceding  pages 
have  sustained  this  statement.  The  Triassic  beds,  as  has 
been  shown,  lie  in  long,  narrow  strips  between  the  Appala- 
chians and  the  coast,  and  spread  widely  over  the  Rocky 
Mountain  region  and  west  nearly  to  the  Pacific.  The 
Jurassic  beds  have  a  similar  wide  distribution  in  the  West, 
though  probably  wanting  in  the  East.  The  Cretaceous 
beds  cover  the  Atlantic  and  Gulf  Borders,  and  a  very  large 
area  over  the  slopes  of  the  Rocky  Mountains  and  the  adja- 
cent plains,  and  the  Pacific  Border  west  of  the  Sierra 
Nevada.  The  eastern  half  of  the  continent  during  the 
Mesozoic  was,  therefore,  receiving  rock  formations  only 
along  its  borders,  while  the  western  half  had  marine  de- 
posits in  progress  over  its  great  interior  and  on  the 
ocean's  border. 

The  American  Mesozoic  deposits  do  not  bear  evidence 
that  they  were  formed  in  a  deep  ocean.  The  Triassic  and 


380  HISTORICAL  GEOLOGY. 

Jurassic  strata  appear  to  have  accumulated  mainly  along 
coasts,  or  in  shallow  waters  off  coasts,  or  in  shallow  estuaries 
or  inland  seas ;  some  of  the  Cretaceous  deposits  indicate  a 
clear  and  open  sea,  but  not  necessarily  one  of  great  depth. 

The  Appalachians  —  the  eastern  mountains  of  the  conti- 
nent— had  been  elevated  before  the  early  Mesozoic  beds 
commenced  to  form  (page  326).  But  the  region  of  the 
Rocky  Mountains  —  the  western  chain  —  was  to  a  great 
extent  still  a  shallow  sea  even  during  the  Cretaceous 
era,  or  when  Mesozoic  time  was  drawing  to  its  close 
(page  376). 

One  strongly  marked  epoch  of  mountain-making,  in 
western  North  America,  occurred  at  the  close  of  the 
Jurassic,  the  Sierra  Nevada  and  other  high  ranges  dating 
from  that  time. 

European  Geography.  —  Europe  has  its  Mesozoic  rocks 
distributed  in  patches,  or  in  several  independent  or  nearly 
independent  areas,  which  show  that  it  retained  its  con- 
dition of  an  archipelago  throughout  Mesozoic  time.  The 
oscillations  of  level,  as  indicated  by  the  variations  in  the 
rocks,  —  variations  both  as  to  the  nature  of  the  beds  and 
their  distribution,  —  were  more  numerous  and  irregular 
than  in  North  America.  The  mountain  elevations  formed, 
however,  were  few  and  small  compared  with  those  that 
followed  either  the  Paleozoic  or  the  Mesozoic.  One  series 
of  disturbances  is  referred  to  the  close  of  the  Triassic,  and 
another  to  that  of  the  Jurassic. 

Among  the  Mesozoic  formations  of  the  European  conti- 
nent there  are  deposits  of  all  kinds  —  those  of  seashores  ; 
of  offshore  shallow  waters  ;  of  moderately  deep,  clear,  and 
open  seas ;  of  inland  seas ;  and  of  marshy,  or  dry  and 
forest-covered,  land. 

Both  in  America  and  Europe  there  were  some  coal  beds 
made,  though  all  of  them  were  comparatively  insignificant, 
except  those  of  western  North  America  in  the  Upper 
Cretaceous ;  even  these  are  inferior  in  extent  to  those  of 
the  Carboniferous. 


MESOZOIC  TIME.  381 

Life.  —  The  Mesozoic  age  witnessed  —  (1)  the  decline 
of  some  ancient  or  Paleozoic  types  of  both  plants  and  ani- 
mals, (2)  the  increase  and  culmination  of  mediaeval  or 
Mesozoic  types,  and  (3)  the  beginning  of  some  of  the 
most  important  of  modern  or  Cenozoic  types. 

1.  Disappearance  of  Ancient  or  Paleozoic  Features.  — 
Among  the  ancient  tribes  of   plants,  several    genera  of 
Ferns  disappear  in  the  Jurassic.     Among  the  old  Brachio- 
pod  tribes,  the  Spirifer  and  Stropliomena  families  end  in 
the  Lias ;  among  Mollusks,  the  Silurian  type  of  Orthoceras 
has  its  last  species  in  the  Triassic ;  in  the  same  era,  the 
Ganoid  Fishes  mostly  lose  the  vertebrated  feature  of  their 
tails,  characterizing  them  in  the  Paleozoic,  and  thus  bear 
evidence  of  progress. 

2.  Progress  in  Mesozoic  Features.  —  The  Cycads,  among 
plants,  were  those  most  characteristic  of   the  Mesozoic  : 
they  afterward   yielded  to  other  kinds,  and  now  are  a 
nearly  extinct  group.     The  Cephalopods,  among  Mollusks, 
existed  in  vast  numbers,  both  those  with  external  shells 
(Tetrabranchs),  as  the  Ammonites,  and  those  without  (Di- 
branchs),  as  the  Belemnites.     The  whole  number  of  species 
of  the  Ammonite  group  thus  far  described  is  almost  5000  ; 
and  the  vast  majority  of  these  belong  to  the  Mesozoic,  the 
Paleozoic  genera  of  the  group  including  comparatively  few 
species.     No  Ammonite  now  exists,  and  the  only  Tetra- 
branch  Cephalopods  now  living   are   six   species  of   the 
genus  Nautilus.     The  whole  number  of  species  of  Cepha- 
lopods living  in  the  course  of  Mesozoic  time  must  have 
been  many  thousand,  since  only  a  part  would  have  been  pre- 
served as  fossils.     The  subkingdom  of  Mollusks,  therefore, 
culminated  in  Mesozoic  time  ;  for  its  highest  class,  that  of 
the  Cephalopods,  was  then  at  its  maximum. 

The  Stegocephala,  or  Labyrinthodonts,  culminated  in 
the  Triassic,  and  became  extinct  at  the  close  of  that  era 
(or  possibly  during  the  Jurassic). 

The  type  of  Reptiles  was  another  that  expanded  and 
reached  its  culmination  —  that  is,  its  maximum  in  number, 


382  HISTORICAL  GEOLOGY. 

variety,  size,  and  rank  of  species,  —  and  commenced  its 
decline  in  Mesozoic  time. 

There  were  huge  swimming  Reptiles,  fishlike  Ichthyo- 
saurs,  and  snakelike  Mosasaurs,  some  of  the  latter  75  or 
80  feet  long,  in  the  place  of  Whales  in  the  sea ;  batlike 
Reptiles,  or  Pterodactyls,  flying  through  the  air;  four- 
footed  Reptiles,  both  grazing  and  carnivorous,  many  of 
them  25  to  50  feet  long,  occupying  the  marshes  and 
estuaries  5  and  great  biped  Reptiles,  or  Dinosaurs,  over 
the  land. 

The  Wealden  formation  of  England  has  afforded  remains 
of  30  or  more  species  of  Dinosaurs,  Crocodiles,  and  Enalio- 
saurs,  most  of  which  were  10  to  50  feet  long,  besides  Ptero- 
dactyls and  Turtles ;  and  many  more  than  this  must  have 
lived,  since  not  all  that  lived  would  have  left  their  remains 
in  the  deposits.  It  is,  however,  not  certain  that  all  the 
species  of  the  Wealden  were  contemporaneous.  To  appre- 
ciate this  peculiarity  of  Mesozoic  time,  it  should  be  con- 
sidered that  in  the  present  age  Great  Britain  has  no  large 
Reptiles.  In  the  whole  torrid  zone  (to  which  large  Rep- 
tiles are  now  mostly  restricted)  there  are  not  much  more 
than  a  dozen  species  over  15  feet  in  length  (Crocodiles, 
and  Snakes  of  the  Python  and  Boa  families),  and  probably 
no  species  reaching  a  length  of  30  feet.  North  America, 
during  the  Jurassic  and  Cretaceous,  appears  to  have  ex- 
ceeded all  the  world  besides,  in  the  number  and  size  of  its 
Reptiles.  Mesozoic  time  is  well  named  the  Age  of  Reptiles. 

The  Birds  of  the  age,  or  at  least  some  of  them,  partook 
of  the  reptilian  features  of  the  time;  some  of  them  having 
long  tails  like  the  associated  Reptiles  (though  feathered 
tails),  and  free  metacarpals ;  and  several  different  groups 
of  Birds  having  reptile-like  teeth.  The  Reptilian  Birds 
and  Pterodactyls  were  the  flying  creatures  of  the  age ; 
the  Ichthyosaurs  and  Plesiosaurs  and  the  like,  the  "great 
whales"  ;  the  Crocodiles  and  Dinosaurs,  the  dominant  life 
of  the  estuaries  and  of  the  land.  Even  the  Mammals  bore 
a  reptilian  character,  being  mostly,  and  probably  exclu- 


LARAMIDE   REVOLUTION.  383 

sively,  Monotremes  and  Marsupials.  The  Monotremes 
resemble  Reptiles  in  being  oviparous,  and  in  numerous 
anatomical  characters.  And  the  Marsupials,  though  vivipa- 
rous, have  not  attained  to  the  typical  mammalian  character 
of  placental  nutrition  of  the  embryo  (page  86). 

3.  Introduction  of  Cenozoic  Features. — Among  plants 
the  first  of  Angiosperms  are  found  in  the  Cretaceous. 
These  become  the  characteristic  plants  of  Cenozoic  time. 

Among  Vertebrates  there  was  a  great  expansion  of  the 
group  of  Teleosts,  or  Osseous  Fishes,  the  species  charac- 
teristic of  earlier  time  having  been  either  Selachians,  Placo- 
derms,  Ganoids,  or  Dipnoans  (page  283).  The  earliest 
species  of  the  modern  genus  Crocodilus  occur  in  the  Creta- 
ceous ;  the  first  of  Birds  in  the  Jurassic  —  Reptilian  Birds; 
the  first  of  Mammals  in  the  Triassic — probably  Mono- 
tremes. 

Of  the  classes  of  Vertebrates,  Fishes  commenced  in  the 
early  Paleozoic,  Amphibia  and  Reptiles  in  the  later  Paleo- 
zoic, Mammals  in  the  early  Mesozoic,  and  Birds  in  the 
middle  Mesozoic. 


DISTURBANCES  CLOSING  MESOZOIC  TIME. 

The  Post-Mesozoic,  or  Laramide,  Revolution.  —  The  close 
of  Mesozoic  time  was  marked  by  the  making  of  the 
greatest  of  American  mountain  systems.  The  Laramide 
mountain  system  extends  along  the  whole  line  of  the  sum- 
mit region  of  the  Rocky  Mountains  from  near  the  Arctic 
Ocean  to  central  Mexico  —  a  distance  exceeding  4000 
miles.  In  the  middle  latitudes  of  the  United  States,  it 
includes  the  Wasatch  Range  of  Utah  and  other  ranges  to 
the  east  as  far  as  the  Front  Range  of  Colorado. 

In  the  Laramide  system,  as  in  the  earlier  Taconic  and 
Appalachian  systems,  there  had  been  an  accumulation  of 
many  thousands  of  feet  of  strata  in  a  geosyncline,  which 
was  in  progress  through  Paleozoic  and  Mesozoic  time;  and 
the  final  orogenic  catastrophe  was  of  the  same  general  nature. 


884         •  HISTORICAL  GEOLOGY. 

It  is  also  probable  that  in  South  America,  at  this  same 
time,  another  system  of  ranges  of  as  great  a  length  was 
made  along  the  Andes,  and  that  consequently  the  moun- 
tain-making movements  of  America  at  the  close  of  the 
Cretaceous  extended  through  nearly  one  third  of  the 
earth's  circumference. 

The  mountain-making  of  this  time  was  accompanied 
by  extensive  igneous  outflows.  Trachyte  eruptions  took 
place  in  the  Wasatch  Mountains. 

The  eruption  of  the  trap  of  the  Deccan  in  India  (page 
189),  the  most  colossal  outflow  of  igneous  rock  of  which 
we  have  evidence,  took  place  at  or  near  the  close  of  the 
Cretaceous. 

Change  of  Fauna  and  Flora.  —  The  disappearance  of 
life  at  this  crisis  was  so  extensive  that  no  species  of  the 
Cretaceous  era,  except  some  Foraminifers  and  land  plants, 
have  yet  been  identified  with  certainty  in  any  rock  of  the 
following  era.  This  is  another  great  feature  in  which 
the  Post-Mesozoic  revolution  was  like  the  Post-Paleozoic. 
Not  only  species,  but  also  many  of  the  families  and  orders 
characteristic  of  the  Mesozoic  disappeared.  Here  ended 
the  reign  of  Reptiles,  all  the  characteristic  Mesozoic  kinds 
—  the  Dinosaurs,  Enaliosaurs,  Pterosaurs,  and  others  — 
becoming  extinct. '  The  Ammonites  also,  and  the  Belem- 
nites,  with  many  of  the  genera  of  other  classes  of  Mollusks, 
disappeared.  Among  plants,  the  Cycads,  which  were  a 
prominent  feature  of  the  early  Cretaceous  forests,  even 
in  Arctic  lands,  later  retreated  southward,  and  became 
confined  to  the  warm-temperate  and  tropical  zones,  where 
the  few  species  now  existing  are  to  be  found. 

As  in  other  such  exterminations,  the  extinction  of  life 
was  not  universal.  The  survival  of  the  genera  and  fami- 
lies proves  that  there  was  no  cataclysmic  break  in  the 
succession  of  life ;  and  some  regions  may  have  suffered 
little  extermination.  All  that  can  be  affirmed  is,  that  the 
fossils  of  the  Tertiary  era,  the  next  after  the  Cretaceous, 
include,  so  far  as  yet  discovered,  no  marine  Cretaceous 


CENOZOIC   TIME.  385 

species,  except  a  few  species  of  Foraminifers,  and  no  Cre- 
taceous species  of  terrestrial  Vertebrates. 

As  to  the  causes  of  so  remarkable  a  change  in  the  life 
of  the  globe,  the  remarks  made  on  page  330  in  reference 
to  the  Appalachian  revolution  are  applicable  here.  Prob- 
ably the  extinction  of  species  at  the  close  of  the  Mesozoic 
was  in  great  degree  due  to  climatic  changes.  The  emer- 
gence from  the  ocean  of  one  third  of  North  America,  and 
probably  of  as  large  a  part  of  South  America,  and  of  large 
portions  of  other  continents,  with  the  resultant  changes 
in  the1  paths  of  ocean  currents,  and  the  formation  of  lofty 
mountain  ranges,  must  have  produced  very  appreciable 
changes  of  climate.  This  may  account  for  much  extinc- 
tion of  species  even  in  regions  where  the  Cretaceous  strata 
and  the  overlying  Tertiary  are  perfectly  conformable. 


IV.    CENOZOIC  TIME. 

CENOZOIC  TIME  includes  two  eras : — 1,  THE  TERTIARY 
ERA,  or  AGE  OF  MAMMALS;  and  2,  THE  QUATERNARY, 
or  AGE  OF  MAN. 

General  Characteristics.  —  In  the  transition  to  this  aeon 
the  life  of  the  world  takes  on  a  new  aspect.  Trees  of 
modern  types  —  Oaks,  Maples,  Beeches,  etc.,  and  Palms 
—  unite  with  Conifers  to  make  the  forests  ;  Mammals  of 
great  variety  and  size  —  Ungulates,  Carnivores,  and  others, 
successors  to  the  small  oviparous  and  semi-oviparous  Mam- 
mals of  the  Mesozoic  —  tenant  the  land,  in  place  of  Rep- 
tiles; typical  Birds  and  Bats  possess  the  air,  in  place  of 
Reptilian  Birds  and  Pterodactyls ;  Whales,  and  Teleosts, 
with  Sharks  mainly  of  modern  type,  occupy  the  waters,  in 
place  of  Enaliosaurs,  and  almost  to  the  exclusion  of  the 
ancient  tribes  of  Cestraciont  Sharks  and  Ganoids.  Finally 
Man  appears,  when  Mammals  are  passing  their  maximum 
in  grade  and  magnitude,  and  becomes  the  dominant  species 
of  the  finished  world. 


386  HISTORICAL   GEOLOGY. 

I.   TERTIARY  ERA. 

GENERAL  CHARACTERISTICS. 

The  Mammals  of  this  age  are  all  extinct  species,  and 
the  animals  of  other  classes  largely  so  ;  the  number  of  liv- 
ing species  of  Invertebrates  varies  from  perhaps  one  per 
cent  in  the  early  part  of  the  age  to  90  at  its  close. 

SUBDIVISIONS. 

The  Tertiary  strata  have  been  divided  by  Lyell  into 
three  groups,  based  upon  the  ratios  between  the  extinct 
species  and  those  still  living,  among  the  Invertebrate  fos- 
sils of  the  respective  beds  :  — 

1.  Eocene  (from  the  Greek  77069,  dawn,  and  /eatw,  recent) : 
species  nearly  all  extinct. 

2.  Miocene  (from  /-tetW,  less,  and  /eatwfc)  :  less  than  half 
the  species  living. 

3.  Pliocene  (from  TrXetW,  more,  and  /caivo^  :  more  than 
half  the  species  living. 

Some  geologists  recognize  a  period  called  Oligocene  be- 
tween Eocene  and  Miocene ;  but  the  Oligocene  strata  are 
here  included  in  the  Eocene. 

The  name  Neocene  is  sometimes  applied  to  the  Miocene 
and  Pliocene  taken  together. 

AMERICAN  GEOGRAPHY:  AREAS  OF  ROCK-MAKING. 

The  changes  of  level  during  the  Laramie  epoch  and  at 
its  close  involved  the  emergence  of  the  great  Interior 
region  of  the  continent.  Of  the  great  mediterranean  sea 
which  had  characterized  the  Cretaceous  period,  the  only 
remnants  were  a  large  bay  on  the  Arctic  shores,  an  exten- 
sion of  the  Gulf  of  Mexico  at  the  south,  and  some  large 
fresh-water  lakes  distributed  over  the  interior.  Marine 
Tertiary  deposits  (exclusive  of  those  in  the  Arctic  regions) 
were  accordingly  confined  to  the  Atlantic  and  Gulf  Border 


TERTIARY  ERA. 


387 


(which  formed  a  single  continuous  area),  and  the  Pacific 
Border.  Fresh-water  deposits  of  great  extent  and  im- 
portance were  made  in  the  lakes  of  the  Interior.  The 
map  (Fig.  433)  shows  the  areas  of  submergence  and  of 
rock-making  in  the  early  and  later  Tertiary  respectively. 
The  areas  vertically  lined  were  under  water  (salt  or  fresh) 
in  the  Eocene  ;  those  horizontally  lined  were  under  water 
in  one  or  both  of  the  later  periods  of  the  Tertiary ;  those 

FIG.  483. 


North  America  in  the  Tertiary  era. 

cross-lined  were  submerged  in  both  early  and  later  Ter- 
tiary time.  As  shown  in  the  map,  the  northward  exten- 
sion of  the  Gulf  of  Mexico  in  the  region  of  the  Mississippi 
was  about  the  same  in  the  Eocene  as  in  the  Cretaceous, 
but  the  shore  line  moved  far  southward  in  the  later  Ter- 
tiary. The  great  lakes  of  the  Eocene  were  in  what  is 
now  the  summit  region  of  the  Rocky  Mountains.  One 
of  them  (U,  on  the  map)  lies  south  of  the  Uinta  Moun- 


388  HISTORICAL   GEOLOGY. 

tains,  between  the  Wasatch  and  the  Front  Ranges  of  Colo- 
rado ;  another,  still  larger  (W,  on  the  map),  lies  north  of 
the  Uinta  Mountains.  In  the  later  Tertiary,  the  lakes  of 
the  summit  region  were  drained,  and  great  lakes  were 
formed  west,  and  especially-  east,  of  that  region.  The 
situation  of  these  lakes  indicates  that  the  Rocky  Mountain 
region  in  general  was  much  less  elevated  at  the  beginning 
of  the  Tertiary  than  at  present. 

ROCKS:  KINDS  AND  DISTRIBUTION. 

The  marine  and  lacustrine  formations  are  independent 
in  their  fossils,  and  are  nowhere  interstratified.  More- 
over, as  geographical  diversity  of  faunas  has  increased 
through  all  geological  time,  the  fossils  of  the  Atlantic  and 
Pacific  Borders  are  almost  wholly  of  different  species.  It 
is  therefore  impossible  to  make  any  exact  correlation  of 
the  formations  of  the  different  regions. 

The  most  northerly  outcrop  of  the  Eocene  on  the  Atlantic 
Border  is  in  New  Jersey.  The  formation  appears  in  that 
state  as  a  narrow  and  interrupted  belt.  It  is  wider  in 
Maryland  and  Virginia,  and  still  wider  in  South  Carolina. 
But  it  is  best  displayed  on  the  Gulf  Border. 

The  Miocene  appears  on  Marthas  Vineyard,  and  dredg- 
ings  on  Georges  Bank  and  the  Grand  Bank  of  New- 
foundland indicate  that  the  deposit  continues  under  the 
shallow  sea  east  of  New  England.  It  extends  continu- 
ously from  New  Jersey  to  North  Carolina,  is  represented 
by  isolated  patches  in  South  Carolina,  is  well  developed 
in  Florida,  and  extends  along  the  Gulf  Border  to  Texas 
and  beyond,  though  partly  covered  by  later  deposits. 

Patches  of  marine  Pliocene  appear  at  various  points 
along  the  Atlantic  Border,  but  the  formation  attains  its 
most  extensive  development  in  Florida  ( Florid ian  forma- 
tion). Along  the  Gulf  Border  lacustrine  deposits  of  late 
Tertiary  age  occur  in  various  places. 

The  Tertiary  rocks  are  generally  but  little  consolidated ; 
they  consist  mostly  of  compacted  sand,  pebbles,  clay,  earth, 


TERTIARY   ERA.  389 

that  was  once  the  mud  of  the  sea  bottom  or  of  estuaries 
or  lakes,  mixed  often  with  shells.  They  are,  indeed, 
such  deposits  as  are  now  forming  along  seashores,  and 
in  shallow  bays,  estuaries,  and  lakes,  or  in  shallow  waters 
off  a  coast.  There  are  also  limestones  made  of  shells,  and 
others  of  corals,  resembling  the  reef  rock  of  coral  seas. 
The  latter  are  found  mainly  in  the  states  bordering  on 
the  Mexican  Gulf.  Another  variety  of  rock  is  buhrstone, 
a  siliceous  rock,  cellular  by  reason  of  the  removal  of  fossil 
shells  by  solution,  used,  on  account  of  its  being  so  hard 
and  at  the  same  time  full  of  irregular  cavities,  for  making 
millstones.  It  occurs  in  the  Eocene  of  South  Carolina, 
Georgia,  and  Alabama.  Beds  of  greensand  and  of  lignite 
or  coal  occur  in  some  of  the  deposits.  Beds  of  Diatoms 
and  Radiolarians  are  sometimes  of  considerable  thickness. 
In  general,  the  Tertiary  rocks  differ  from  those  of  earlier 
periods  in  that  the  character  of  the  beds  of  the  same  hori- 
zon is  apt  to  vary  from  mile  to  mile,  instead  of  persisting 
over  large  areas.  There  are,  however,  some  exceptional 
cases  of  Tertiary  beds  whose  character  is  nearly  uniform 
over  considerable  areas.  The  lacustrine  beds  of  the  Inte- 
rior are  remarkable  for  the  treasures  of  fossil  Mammals 
which  they  have  yielded.  Local  lignitic  beds  of  lacus- 
trine origin  are  scattered  over  various  parts  of  the  coun- 
try. One  at  Brandon,  Vermont,  supposed  to  be  of  Eocene 
age,  is  famous  for  the  fossils  it  has  yielded. 

The  Tertiary  of  Great  Britain  (11,  on  map,  page  295) 
occurs  mostly  in  the  southeastern  part  of  England,  in  the 
London  basin,  and  on  the  southern  and  eastern  borders  of 
the  island,  adjoining  the  Cretaceous.  The  large  areas  are 
mostly  Eocene  (including  Oligocene) ;  a  narrow  strip  along 
the  coast  of  Norfolk  and  Suffolk  is  Pliocene. 

On  the  continent  of  Europe,  the  Paris  basin  is  noted 
for  its  Eocene  strata  and  their  fossil  Mammals.  Other 
Tertiary  areas  are  those  of  the  Pyrenean  and  Mediterra- 
nean regions,  those  of  Switzerland,  of  Austria,  etc.  Some 
of  the  marine  Eocene  beds  contain  Rhizopods  (p.  62) 


390  HISTORICAL  GEOLOGY. 

having  the  shape  of  a  coin,  called  Nummulites  (from  the 
Latin  nummus,  a  coin).  One  is  here  figured,  natural 
size  ;  the  exterior  of  one  half  has  been  removed  to  show 
the  cells  within.  Occasionally  the  beds  are  so  far  made 
up  of  these  Nummulites  that  the  rock  is  called  Nummulitic 
Limestone. 

These  marine  Eocene  strata  spread  very  widely  over 
Europe,  northern  Africa,  and  Asia  —  occurring  in  the 
Pyrenees,  forming  some  of  their  summits ; 
in  the  Alps  to  a  height  of  more  than  10,000 
feet ;  in  the  Carpathians ;  in  Algeria  ;  in 
Egypt,  where  the  most  noted  pyramids 
were  made  of  Nummulitic  Limestone;  in 
Persia;  in  the  Himalayas,  to  a  height  of 

more  than  20>000  feet •>    in  Japan  and  the 
East  Indies.     The  later  Tertiary  formations 
are  much  more  limited  in  distribution,  and  many  are  of 
terrestrial  or  fresh-water  origin. 

The  rocks  are  similar  to  those  of  North  America,  but 
include  more  of  hard  sandstone  and  limestone.  The  sand- 
stone is  a  very  common  building  stone  in  different  parts 
of  Europe,  being  soft  enough  to  be  worked  with  facility, 
yet  generally  hardening  on  exposure,  owing  to  the  fact 
that  it  contains  calcareous  particles  (triturated  shells), 
which  render  the  percolating  waters  or  rain  calcareous,  so 
that  on  evaporating  they  produce  a  calcareous  deposit,  as 
a  cement,  among  the  grains  of  sand. 

LIFE. 

PLANTS. 

The  great  feature  of  the  Tertiary  vegetation  is  the 
prevalence  of  Angiosperms,  a  class  of  plants  which,  thus 
far,  is  unknown  before  the  Cretaceous.  Leaves  of  Oak, 
Poplar,  Maple,  Hickory,  Dogwood,  Mulberry,  Magnolia, 
Cinnamon,  Fig,  Sycamore,  Willow,  and  many  others,  rep- 
resent the  Dicotyledons,  while  the  Monocotyledons  are  rep- 


TERTIARY   ERA. 


391 


resented  by  numerous  Palms.  There  are  also  remains  of 
Conifers.  Nuts  are  common  in  some  beds  —  as  at  Bran- 
don, Vermont.  Fig.  435  is  the  leaf  of  an  Oak  ;  Fig.  436, 
of  a  species  of  Cinnamon  ;  Fig.  439,  of  a  Palm ;  Fig.  437, 
the  nut  of  a  Beech,  much  like  that  of  the  common  Beech; 
Fig.  438,  another  nut,  from  Brandon,  of  unknown  rela- 
tions. 

FIGS.  435-439. 


DICOTYLEDONS:  Fig.  435,  Quercus  myrtifolia;  436,  Cinnamomum  Mississippiense ; 
437,  Fagus  ferruginea ;  438,  Carpolithes  irregularis.  —  MONOCOTYLEDON  :  Fig.  439,  Ca- 
lamopsis  Danae. 

The  Eocene  Plants  of  Great  Britain  included  Palms, 
and  among  those  of  central  and  southern  Europe  there 
were  many  species  related  to  the  trees  of  Australia  ;  while 
the  Miocene  and  Pliocene  floras  of  Europe  (especially  the 
former)  had  much  similarity  to  the  flora  of  America. 

The  microscopic  plants  which  form  siliceous  shells, 
called  Diatoms  (Figs.  143-148,  page  88),  make  extensive 
deposits  in  some  places.  One  stratum  near  Richmond,  Vir- 


392 


HISTORICAL    GEOLOGY. 


ginia,  is  30  feet  thick,  and  is  many  miles  in  extent ;  another, 
near  Monterey,  California,  is  50  feet  thick,  and  the  mate- 
rial is  as  white  and  fine  as  chalk,  which  it  resembles  in  ap- 
pearance ;  another,  near  Bilin  in  Bohemia,  is  14  feet  thick. 


DIATOMS  (and  other  organisms)  from  Richmond  diatomaceous  bed  :  a,  Pinnularia  peregrina ; 
b,  c,  Odontidium  pinmilatum ;  d,  Grammatophora  marina;  e,  Spongiolithis  appendic- 
ulata ;  /,  Melosira  sulcata ;  g,  same,  transverse  section ;  h,  Actinocyclus  Ehrenbergii ; 
i,  Coscinodiscus  apiculatus ;  j,  Triceratium  obtusum  ;  k,  Actinoptychus  undulatus; 
Z,  Dictyocha  crux ;  m,  Dictyocha;  n,  fragment  of  Actinoptychus  senarius;  o,  Navicula; 
p,  fragment  of  Coscinodiscus  gigas. 

The  material  from  the  latter  place  was  used  as  a  polish- 
ing powder  (and  called  Tripoli,  or  polishing  slate)  long 
before  it  was  known  that  its  fine  grit  was  owing  to  the 
remains  of  microscopic  life.  Ehrenberg  has  calculated 
that  a  cubic  inch  of  the  fine  earthy  rock  contains  about 


TERTIARY  ERA.  393 

forty-one  thousand  millions  of  organisms.  Such  accumu- 
lations of  Diatoms  are  made  both  in  fresh  waters  and 
salt,  and  in  those  of  the  ocean  at  all  depths.  A  group  of 
Diatoms  from  the  Richmond  bed  is  shown  in  Fig.  440. 

ANIMALS. 

The  most  prominent  fact  with  regard  to  the  Tertiary 
Invertebrates  is  their  general  resemblance  to  modern  spe- 
cies. Although  a  number  of  the  genera  are  extinct,  and 
nearly  every  Eocene  species,  there  is  still  a  modern  look 
in  the  remains,  and  the  specimens  have  often  the  fresh- 
ness of  shells  from  a  modern  beach.  Only  a  special  stu- 
dent of  the  Mollusca  can  distinguish  the  Tertiary  species 
from  those  now  living.  After  the  Eocene,  species  of  the 
present  time  begin  to  be  abundant.  The  common  Oyster 
and  Clam  have  been  found  fossil  in  deposits  believed  to 
be  of  Miocene  age. 

Remains  of  Insects  are  more  abundant  and  varied  than 
in  any  previous  era.  All  the  important  orders  are  repre- 
sented, including  the  Lepidopters  (Moths  and  Butterflies), 
which  probably  do  not  occur  in  any  earlier  formation. 
More  than  2000  species  of  Insects,  in  wonderfully  perfect 
state  of  preservation,  have  been  obtained  from  the  Amber 
of  the  Baltic  shores.  The  Amber  is  a  fossil  resin,  derived 
from  Coniferous  trees  of  the  Upper  Eocene  (Oligocene) 
period ;  and  the  Insects  were  caught  in  .the  resin  while 
it  was  still  liquid,  and  thus  effectually  embalmed.  Flo- 
rissant, Colorado,  is  a  famous  locality  for  Eocene  Insects  ; 
and  Oeningen  in  Switzerland,  and  Radoboj  in  Croatia,  are 
among  the  richest  Miocene  localities. 

With  regard  to  Vertebrates,  the  points  of  special  inter- 
est are  the  following  :  — 

1.  In  the  class  of  Fishes  :  (1)  Teleosts,  or  Fishes  allied 
to  the  Perch  a-nd  Salmon,  are,  as  already  stated,  the  preva- 
lent group  ;  (2)  sharp-toothed  Sharks  are  abundant,  some 
of  them  having  teeth  6  inches  long  and  nearly  5  inches 
broad.  The  teeth  of  Sharks  are  the  most  durable  part  of 


394 


HISTORICAL  GEOLOGY. 


442 


FIGS.  441,  442. 


441 


the  skeleton ;  they  are  very  abundant  in  both  Eocene  and 
Miocene  beds.  Fig.  441  represents  a  tooth  of  Carcharodon 
angmtidens.  The  larger  teeth  above  alluded  to  belong  to 
Carcharodon  megalodon,  and  are  found  at  different  places 
on  the  Atlantic  Border  from  Marthas  Vineyard  southward. 
Fig.  442  represents  the  tooth  of  another  common  kind  of 
Shark,  a  species  of  Lamna,  from  the  Eocene. 

2.  In  the  class  of  Amphibians:  Only  the  modern  groups 
of  Salamanders  and  Toads  and 
Frogs  are  represented. 

8.  In  the  class  of  Reptiles : 
Crocodiles  and  Turtles  are  nu- 
merous. The  shell  of  one  of  the 
Pliocene  turtles,  found  fossil  in 
India,  had  a  length  of  12  feet, 
and  the  animal  is  supposed  to 
have  been  20  feet  long. 

4.  In  the  class  of  Birds :  The 
species  found  are  not  long-tailed, 
or  in  any  respect  reptilian,  but 
resemble  modern  Birds  ;  they  are 
related  to   the    Geese,    Pelicans, 
Petrels,  Herons,  Rails,  Pheasants, 
Eagles,    Owls,    Doves,    Parrots, 
Woodpeckers,      Sparrows,      and 
other  kinds. 

5.  In  the  class  of  Mammals  : 
The    typical    (Placental)    Mam- 
mals attain  a  remarkable  develop- 
ment.    In  the  Mesozoic,  probably  all  the  Mammalian  re- 
mains are  those  of  Marsupials  and  Monotremes.     But  the 
very  earliest  Eocene  deposits  contain  remains  of  a  number 
of  orders  of  Placental  Mammals.     Before  the  close  of  the 
Eocene,  most  of  the  principal  orders  now  in  existence  had 
already  appeared,  in  addition  to  some  orders  now  extinct. 
There  were  already,  in  the  Eocene,  Insectivores,  Bats,  Car- 
nivores, Lemurs,  Rodents,  Ungulates,  and  Whales.    Before 


SELACHIANS:  FIG.  441,  tooth  of  Car 
charodon  angustidens ;  442,  Lam 
na  elegans. 


TERTIARY    ERA. 


395 


the  close  of  the  Miocene,  Edentates  and  Monkeys  were 
added  to  the  list. 

Many  of  the  Eocene  Mammals  exhibit  remarkably  gen- 
eralized, or  primitive,  characters.  They  have  the  typical 
number  of  teeth  (44),  and  have  the  molars  of  simple  form 
with  crowns  showing  three  tubercles.  Their  feet  are 
five-toed,  and  plantigrade  (i.e.,  the  entire  foot,  even  to 
the  wrist  or  heel,  rests  upon  the  ground)  ;  and  the  bones 

FIG.  448. 


UNGULATE:  Phenacodus  primaevus,  Xj'g,  a,  fore  foot;  6,  hind  foot. 

of  the  wrist  and  ankle  are  in  parallel  series.  The  two 
bones  of  the  forearm  (radius  and  ulna),  and  the  corre- 
sponding bones  of  the  leg,  are  distinct  from  each  other. 
In  later  times,  some  of  the  Ungulates  have  departed  most 
widely  from  these  primitive  characters,  as  may  be  seen  in 
the  Horse,  with  its  smaller  number  of  teeth,  complicated 
enamel  folds  in  its  molars,  fingers  and  toes  reduced  to 
one,  only  the  finger  nails  and  toe  nails  (hoofs)  reaching 
the  ground,  bones  of  wrist  and  ankle  interlocking,  bones 
of  the  forearm  united  (the  ulna  becoming  little  more  than 


396  HISTORICAL   GEOLOGY. 

a  rudiment),  and  the  leg  showing  a  like  modification.  The 
number  of  teeth  has  suffered  reduction  in  almost  all  the 
later  Mammals  ;  but  others  of  the  primitive  characteristics 
which  have  been  mentioned  are  retained  in  many  groups 
of  modern  Mammals  (some  of  them  in  Man  himself). 

In  the  earliest  Eocene,  some  of  the  representatives  of  the 
Ungulate  series  exhibited  all  the  primitive  characters 
just  enumerated.  Such  a  primitive  Ungulate  as  is  shown 
in  Fig.  443  differs  but  little  from  the  types  of  Carnivores 
(Creodonts)  that  existed  in  the  same  early  Eocene  strata. 
The  various  orders  had  not  then  become  as  strongly  differ- 
entiated as  they  were  destined  to  become  in  later  times. 
Before  the  close  of  the  Eocene,  Ungulates  and  Carnivores 
had  diverged  much  further  from  each  other,  and  presented 
themselves  in  much  more  characteristic  forms.  There 
is  perhaps  no  finer  illustration  of  the  theory  of  evolution 
than  that  which  is  presented  in  the  progress  of  the  Ungu- 
lates from  the  extremely  generalized  forms  of  the  earliest 
Eocene  to  such  specialized  forms  as  the  Horses  and 
Ruminants  of  to-day. 

Another  noteworthy  general  fact  in  regard  to  the  Mam- 
mals of  the  early  Tertiary  is  the  small  size  of  their  brains, 
as  compared  with  later  species,  as  illustrated  in  Figs. 
444-446. 

Cuvier  first  made  known  to  science  the  existence  of 
Tertiary  Mammals  of  extinct  species.  The  remains  from 
the  earthy  beds  about  Paris  had  been  long  known,  and  were 
thought  to  be  those  of  modern  beasts.  But,  by  careful  study 
and  comparison  with  living  animals,  Cuvier  was  enabled 
to  bring  the  scattered  bones  together  into  skeletons,  as- 
certain the  orders  to  which  they  belonged,  and  determine 
the  food  and  mode  of  life  of  the  extinct  species.  Cuvier 
acquired  his  skill  in  the  interpretation  of  fossils  by 
observing  the  mutual  dependence  which  subsists  between 
all  parts  of  a  skeleton,  and,  in  fact,  all  parts  of  an  animal. 
A  sharp  claw  is  evidence  that  the  animal  has  trenchant 
or  cutting  molar  teeth,  and  is  a  flesh-eater  ;  a  hoof,  that 


TERTIARY   ERA. 


397 


he  has  broad  molars,  and  is  a  grazing  species  ;  and,  fur- 
ther, almost  every  bone  has  some  modification  showing 
the  group  of  species  to  which  it  belongs,  and  may  thus  be 
an  indication,  in  the  hands  of  one  well  versed  in  the  sub- 
ject, of  the  special  type  of  the  animal,  and  of  its  structure, 
even  to  its  stomach  within  and  its  hide  without.  In  thus 
applying  comparative  anatomy  to  the  interpretation  of 
fossils,  Cuvier  laid  the  foundation  of  a  new  department 
of  science — paleontology. 


444 


FIGS.  444-446. 
445 


Illustrations  of  relative  sizes  of  brains:  Fig.  444,  Dinoceras  (Eocene);  445,  Titanotherium 
(Miocene) ;  446,  Equus  (Recent). 

One  genus  of  these  Paris  beasts  from  the  middle  Eocene 
beds  is  named  Paloeotherium,  from  the  Greek  TraXato?, 
ancient,  and  Oripiov,  wild  beast.  It  is  related  to  the  modern 
Tapirs,  though  it  had  a  longer  neck  and  a  more  slender 
and  graceful  form.  It  was  in  some  respects  intermediate 
between  the  Tapir  and  the  Horse.  The  largest  species 
of  the  genus  was  of  the  size  of  a  Horse.  Palceotlierium 
was  a  representative  of  the  Perissodactyls  —  Ungulates 
having  an  odd  number  of  toes  (at  least  in  the  hind  feet), 


398 


HISTORICAL   GEOLOGY. 


and  the  middle  toe  the  largest.  Anoplotherium,  Xiphodon, 
and  others  of  the  Paris  fossils,  were  representatives  of 
the  Artiodactyls,  having  the  number  of  toes  even,  and  the 
third  and  fourth  toes  about  equally  developed,  as  in  the 
Hog,  Deer,  Ox,  etc.  It  is  noteworthy  that  these  two 
principal  suborders  of  modern  Ungulates  had  become  dif- 
ferentiated before  the  close  of  the  Eocene.  The  fauna  of 
the  Paris  Eocene  included  also  some  Carnivores,  a  Bat, 
and  an  Opossum. 

FIG.  447. 


UNGULATE  :  Dinoceras  mirabile,  x  |. 

The  marine  Eocene  deposits  of  the  Gulf  States  have 
afforded  remains  of  a  species  of  Whale  of  great  length, 
called  Zeuglodon,  from  £evy\r),  yoke,  and  oSou?,  tooth,  in 
allusion  to  the  fact  that  some  of  the  teeth  have  two  long 
fangs  which  give  them  a  yokelike  shape.  The  bones  occur 
in  many  places  in  the  Gulf  States,  and  in  Alabama  the  ver- 
tebrae were  formerly  so  abundant  as  to  have  been  built 
up  into  stone  walls,  or  burned  to  rid  the  fields  of  them. 
The  living  animal  was  probably  70  feet  in  length.  One 


TERTIARY   ERA. 


399 


of  the  larger  vertebrae  measures  a  foot  and  a  half  in  length 
and  a  foot  in  diameter. 

The  lacustrine  deposits  of  the  Rocky  Mountain  region 
have  yielded  a  wonderfully  rich  harvest  of  Mammalian 
remains.  The  remarkably  primitive  Ungulate,  Phenaco- 
dus,  shown  in  Fig.  443,  is  from  the  lower  Eocene  (Wasatch) 
beds  of  Wyoming.  From  the  Middle  Eocene  (Bridger 
group)  of  the  Green  River  basin,  north  of  the  Uinta 
Mountains,  a  large  number  of  species  have  been  obtained. 
The  skull  of  one  kind,  of  elephantine  size,  having  six 
horn  cores,  and  called  by  Marsh  Dinoceras,  in  allusion  to 


FIGS.  448-451. 


449 


EQUID*::  Fig.  448,  fore  foot  of  Orohippus  (Eocene);  449,  Anchitherium  (Miocene);  450, 
Hipparion  (Pliocene);  451,  Equus  (Recent). 

its  horns,  is  represented  in  Fig.  447.  There  was  also  one 
of  the  earliest  genera  of  the  Horse  tribe,  called  Orohippus  ; 
and  it  is  remarkable  that  these  Eocene  Horses  had  four 
usable  toes  in  the  fore  feet  (Fig.  448),  and  three  in  the 
hind  feet,  instead  of  the  single  toe  of  the  modern  Horse. 
The  relation  of  the  foot  of  the  latter  to  different  kinds 
of  Tertiary  Horses  is  illustrated  in  Figs.  448-451. 

In  Fig.  451  it  is  shown  that  the  modern  Horse  has  one 
usable  toe,  the  third,  and  rudiments  of  two  others,  the 
second  and  fourth,  in  what  are  called  the  splint  bones. 
In  Hipparion,  of  the  Pliocene  (Fig.  450),  the  second  and 
fourth  have  hoofs,  but  they  are  so  short  as  not  ordinarily 


400  HISTORICAL   GEOLOGY. 

to  reach  the  ground.  In  Anchitherium,  of  the  Miocene 
(Fig.  449),  the  second  and  fourth  toes  come  to  the  ground, 
and  are  therefore  usable.  In  Orohippus  (Fig.  448),  which 
was  not  larger  than  a  Fox,  there  are  four  toes,  and  all  are 
usable. 

Other  Wyoming  species  are  related  to  the  Tapir  and 
Hog,  some  approaching  in  characters  the  Paris  Palceo- 
therium.  There  were  also  Lemurs,  Creodonts  (animals  re- 
lated to  Carnivores  in  form  and  habit,  but  retaining  some 
of  the  primitive  characteristics  of  Insectivores),  Bats, 
Moles,  and  other  Insectivores,  Rodents,  and  Marsupials. 

The  Lower  Miocene  beds  of  the  "  Bad  Lands,"  on  the 
White  River  (regarded  by  W.  B.  Scott  as  Oligocene), 

FIG.  452. 


UNGULATE:  tooth  of  Titanotherfum  Prouti,  x  £. 


have  afforded  remains  of  other  Mammals.  Among  them 
are  several  Carnivores  related  somewhat  to  the  Hyena, 
Dog,  and  Panther  ;  many  Ungulates,  including  several 
species  of  Rhinoceros,  and  forms  approaching  the  Tapir, 
Peccary,  Deer,  Camel,  Horse  ;  also  several  genera  of 
Rodents.  Fig.  452  represents  a  tooth  of  Titanotherium, 
an  animal  related  to  the  Tapir  and  Palceotherium,  but  of 
elephantine  size,  standing  probably  7  or  8  feet  high.  The 
skull  in  this  genus  shows  a  pair  of  large  horn  cores  on 
the  boundary  between  the  frontal  and  the  nasal  bones  — 
a  structure  not  found  in  any  Perissodactyl  now  living. 
Horns  in  pairs  are  at  present  confined  to  the  Artiodactyls. 
Fig.  453  represents  the  skull  of  another  Miocene  Mam- 
mal, called  Oreodon*  which  is  intermediate  between  the 


TERTIARY    ERA. 


401 


Deer,  Camel,  and  Hog.  Remains  of  a  Camel  and  Rhi- 
noceros, and  of  some  tapir-like  beasts,  have  been  found 
in  the  Miocene  of  the  Atlantic  Border. 


FIG.  453. 


Fro.  454. 


UNGULATE  :  Oreodon  gracilis. 

In  the  Upper  Miocene  beds  (Loup  Fork  group)  of 
Nebraska  and  other  localities  (considered  Pliocene  by 
some  geologists),  still  other 
species  occur,  including  Camels, 
a  Rhinoceros,  a  Mastodon, 
Horses,  Deer,  a  Wolf,  a  Tiger, 
Weasels  —  a  range  of  species 
quite  Oriental  in  character. 

Among  Mammals  of  the  Eu- 
ropean Miocene  there  were 
Horses,  Rhinoceroses,  Deer,  and 
other  Ungulates,  including  two 
genera  (^Dinotherium  and  Masto- 
don) of  the  remarkable  suborder 
of  Proboscideans.  In  the  genus 
Dinotherium,  the  tusks  were  in 
the  lower  jaw,  as  shown  in  Fig.  454.  The  Elephant,  now 
the  only  surviving  genus  of  Proboscideans,  did  not  appear 


PROBOSCIDEAN  :  Dinotherium  gigan- 
teum    x    1. 


402  HISTORICAL   GEOLOGY. 

until  the  Pliocene.     The  earliest  Oxen  occur  in  the  Plio- 
cene of  Europe  and  India. 

There  were  also  in  the  European  Miocene  and  Pliocene 
many  Carnivores,  besides  Monkeys,  Aard-varks,  etc. 

GENERAL  OBSERVATIONS. 

Geography :  Mountain-making.  —  The  Tertiary  era  was 
characterized,  both  in  the  Old  World  and  the  New,  (1) 
by  the  approximate  completion  of  the  work  of  rock-mak- 
ing on  the  borders  of  the  continents,  so  that  the  land 
areas  gained  nearly  the  outlines  which  they  have  at  pres- 
ent; (2)  by  great  erogenic  movements,  in  which  most  of 
the  loftiest  mountain  ranges  of  the  globe  acquired  at  least 
a  considerable  part  of  their  present  elevation. 

In  North  America,  by  the  close  of  the  Tertiary,  the  con- 
tinent had  reached  substantially  its  present  extent,  along 
the  Atlantic,  Gulf,  and  Pacific  Borders,  and  the  great  lakes 
of  the  Rocky  Mountain  region  had  been  drained. 

At  the  close  of  the  Miocene,  the  Coast  Range  of  Oregon 
and  California  experienced  a  second  uplift  (see  page  362), 
Cretaceous,  Eocene,  and  Miocene  strata  being  tilted  and 
more  or  less  folded. 

But  the  most  remarkable  geographical  change  in  North 
America  was  a  great  geanticlinal  movement  affecting  the 
whole  Rocky  Mountain  region.  The  long  persistence  of 
lakes  in  the  Rocky  Mountain  region  indicates  that  the 
elevation  was  not  great  in  the  Eocene  and  Miocene,  and 
that  a  large  part  of  the  movement  took  place  in  Pliocene 
time.  The  Cretaceous  beds  (which  must  have  been  origi- 
nally at  or  near  sea  level)  have  an  altitude  (in  spite  of 
great  denudation)  of  13,000  feet  in  parts  of  the  United 
States,  10,000  feet  in  central  Mexico,  and  4000  feet  in 
British  America  near  the  Arctic  Ocean.  This  elevation  is 
partly  due  to  the  post-Mesozoic  orogenic  movement  (Lara- 
mide  revolution)  described  on  page  383,  and  partly  to  the 
Tertiary  geanticlinal  movement.  But  nearly  horizontal 
Tertiary  strata  are  found  in  Wyoming,  north  of  the  Uinta 


TERTIARY   ERA.  403 

Mountains,  at  an  elevation  of  more  than  9000  feet,  and  in 
the  High  Plateaus  of  Utah  at  an  elevation  of  more  than 
10,000  feet. 

The  Sierra  Nevada  (as  explained  on  page  362)  was 
formed  by  the  crushing  of  a  geosyncline  at  the  close  of 
the  Jurassic.  But  much  of  the  height  then  gained  was 
doubtless  lost  by  erosion.  Le  Conte  has  shown  by  a  study 
of  the  river  valleys  that  a  large  part  of  the  present  altitude 
of  that  range  is  due  to  its  participation  in  the  great  Rocky 
Mountain  geanticlinal  movement.  The  old  river  valleys 
of  the  region  have  been  filled  up  and  obliterated  by  basaltic 
eruptions  whose  date  was  not  far  from  the  close  of  the 
Tertiary.  The  fact  that  the  new  valleys  have  been  carved 
to  a  far  greater  depth  than  the  old  ones  indicates  that  the 
region  has  been  greatly  elevated. 

The  formation  of  the  great  geanticline  was  accompanied 
by  the  development  of  numerous  faults,  some  of  them  hav- 
ing a  throw  of  thousands  of  feet,  having  in  general  a  trend 
approximately  parallel  with  the  axis  of  the  mountain  chain, 
and  distributed  over  the  whole  breadth  of  the  Great  Basin, 
from  the  Sierra  Nevada  to  the  Wasatch,  and  southward 
over  the  High  Plateaus  of  Utah.  The  steep  eastern  front 
of  the  Sierra  is  determined  by  one  of  these  great  faults. 

In  the  Orient,  the  Eocene  era  was  one  of  very  extensive 
submergence  of  the  land,  as  shown  by  the  distribution  of 
the  Nummulitic  beds  over  Europe,  Asia,  and  northern 
Africa,  as  stated  on  page  390.  Before  the  close  of  the 
Eocene,  the  greater  part  of  these  continental  seas  became 
dry  land,  and  in  general  continued  so  afterwards;  for  the 
marine  Miocene  and  Pliocene  are,  comparatively,  of  limited 
extent.  Many  of  the  principal  mountain  ranges  of  Europe 
and  Asia,  as  the  Pyrenees,  Alps,  Carpathians,  Himalayas, 
etc.,  received  in  Tertiary  time  a  large  part  of  their  eleva- 
tion. The  Pyrenees  were  elevated  at  the  close  of  the 
Eocene.  The  region  of  the  Alps  had  experienced  a  num- 
ber of  orogenic  disturbances  in  former  times,  one  of  these 
epochs  of  disturbance  being  at  the  close  of  the  Paleozoic; 


404  HISTORICAL   GEOLOGY. 

but  the  great  movement  which  formed  the  Alps  of  to-day 
dates  from  the  close  of  the  Miocene.  The  Jura  and  the 
Carpathians  belong  to  the  same  period  of  disturbance  which 
produced  the  Alps.  The  Apennines  give  evidence  of  one 
erogenic  movement  at  the  close  of  the  Eocene  and  another 
at  the  close  of  the  Miocene.  The  Himalayas  have  Num- 
mulitic  (Eocene)  beds,  at  a  height  of  more  than  20,000 
feet;  so  that  this  great  chain,  although  it  shows  in  the 
region  of  the  Indus  evidence  of  some  disturbance  before 
the  Eocene,  was  not  completed  till  after  the  deposition  of 
the  Nummulitic  Limestones.  Whether  the  principal  move- 
ment of  elevation  was  at  the  close  of  the  Eocene,  or  at  the 
close  of  the  Miocene,  has  not  been  certainly  shown.  Some 
elevation  occurred  even  after  the  deposit  of  the  Pliocene 
beds  of  the  Siwalik  Hills. 

Thus,  when  the  Tertiary  era  closed,  the  globe  had  ac- 
quired substantially  its  present  features. 

The  great  geanticlinal  movements  affecting  large  areas 
of  the  continents  probably  had  their  counterpart  in  a  sub- 
sidence of  great  parts  of  the  ocean  bottom  —  the  Coral 
Island  subsidence  (see  page  104). 

Gondwana-land,  connecting  India  with  southern  Africa 
in  late  Paleozoic  time  and  throughout  Mesozoic  time,  ac- 
cording to  Oldham,  sank  below  the  sea  in  the  Tertiary. 

Igneous  Eruptions.  —  A  great  period  of  igneous  erup- 
tions in  western  North  America  commenced  at  the  close  of 
the  Cretaceous  (Laramide  revolution),  culminated  in  the 
Miocene,  and  may  be  said  to  have  continued  with  diminish- 
ing intensity  to  the  present  time,  some  of  the  volcanic 
cones  being  not  yet  extinct.  The  Tertiary  eruptions  were 
in  large  part  fissure  eruptions  (page  189),  though  great 
volcanic  cones  were  also  formed.  The  area  in  the  north- 
western United  States  covered  by  sheets  of  eruptive  rock 
is  only  surpassed  by  that  of  the  somewhat  earlier  (Cre- 
taceous) outflows  in  the  Deccan. 

Climate.  —  During  the  Eocene,  Palms  abounded  in  Great 
Britain  —  evidence  of  a  subtropical  or  warm-temperate 


QUATERNARY   BRA.  405 

climate  in  that  latitude;  and  the  Arctic  regions  had  forests 
consisting  of  Beech,  Plantain,  Willow,  Oak,  Poplar,  Wal- 
nut, Magnolia,  Redwood,  showing  a  mean  temperature  of 
at  least  48°  F.  (Heer).  In  the  Miocene,  southern  Europe 
had  a  subtropical  climate,  but  England  had  lost  its  Palms 
and  was  cooler. 

In  North  America,  in  the  early  Tertiary,  a  warm-tem- 
perate climate  must  have  extended  to  the  northern  boundary 
of  the  United  States,  as  shown  by  the  fossil  plants  at 
Brandon,  Vermont,  and  in  other  localities. 

The  Camels,  Rhinoceroses,  and  other  animals  of  the 
upper  Miocene  of  Nebraska,  seem  to  prove  that  a  warm- 
temperate  climate  prevailed  there  in  that  period. 

It  is  therefore  plain  that  the  earth  had  not  as  great  a 
diversity  of  zones  of  climate  in  the  early  Tertiary  as  now; 
and  that  Europe  was  not  very  much  colder  in  the  Eocene 
period  than  in  the  Jurassic  era. 

* 
II.  QUATERNARY  ERA. 

General  Characteristics.  —  The  Quaternary  age  was  re- 
markable (1)  for  oscillations  of  level  and  climatic  changes 
in  high  latitudes  both  north  and  south  of  the  equator ; 
(2)  for  the  culmination  of  the  type  of  brute  Mammals ; 
and  (3)  for  the  appearance  of  Man  on  the  globe. 

Periods.  —  The  periods  are  three :  — 

1.  The  GLACIAL,  or  the  period  when,  over  the  higher 
latitudes,  large  areas  of  the  continents  stood  at  an  alti- 
tude considerably  greater  than  at  present,  and  experienced 
a  colder  climate,  with  immense  development  of  glaciers. 

2.  The  CHAMPLAIN,  when  the  ice  disappeared,  and  the 
same  high-latitude  portions  of  the  continent,  and  to  a  less 
extent  other  regions,  were  below  their  present  level,  and 
became  covered  by  extensive  fluvial  and  lacustrine  forma- 
tions, and  along  seacoasts  by  marine  formations. 

3.  The  RECENT  period,  begun  by  a  rising  of  the  land 
nearly  or  quite  to  its  present  level. 


406  HISTORICAL   GEOLOGY. 

The  Glacial  and  the  Champlain  periods  taken  together 
are  often  called  the  Pleistocene.  They  are  in  general  not 
clearly  differentiated  from  each  other  except  in  the  high- 
latitude  regions  which  experienced  the  remarkable  changes 
of  level  and  climate  above  mentioned. 


Physical  History  of  the  Quaternary. 

1.   GLACIAL  PERIOD. 

The  Drift.  —  The  most  characteristic  phenomenon  con- 
nected with  the  Glacial  period  is  a  peculiar  and  wide- 
spread deposit  over  the  continents,  which  gives  evidence  in 
general  of  transportation  from  the  higher  latitudes  to  the 
lower. 

The  transported  material  consists  of  earth,  gravel,  stones, 
and  bowlders ;  and  includes,  in  America,  nearly  all  the 
earth,  as  well  as  stones,  of  the  surface  in  the  latitude  of 
New,  England  and  farther  north.  It  extends  over  hills  and 
valleys,  and  varies  in  depth  from  a  few  feet  to  hundreds. 
A  large  part  of  the  material  is  in  an  unstratified  condition, 
large  stones  and  small,  pebbles  and  sand,  being  mingled 
pellmell.  Part,  especially  that  in  the  valleys  or  depres- 
sions of  the  surface,  is  stratified,  and  thus  bears  evidence 
of  deposition  by  flowing  waters,  like  fluvial  and  lacustrine 
formations.  But  the  greater  part  of  the  stratified  drift 
belongs  to  the  Champlain  period. 

The  transported  material  is  called  Drift,  and  the  unstrati- 
fied part  of  it  till  (a  word  of  uncertain  origin  first  applied 
to  this  deposit  in  Scotland).  The  till,  especially  its  lower 
part,  is  often  a  clayey  earth,  or  a  clayey  mixture  of  earth 
and  stones  with  frequent  bowlders,  called  the  bowlder  clay  ; 
it  is  in  general  firmly  compacted. 

The  traveled  stones  are  of  all  dimensions,  from  that  of 
a  small  pebble  to  masses  as  large  as  a  moderate-sized 
house.  One  in  Nottingham,  New  Hampshire,  is  62,  40, 
and  40  feet  in  its  diameters,  and  is  estimated  to  weigh 
about  6000  tons.  A  still  larger  one  in  Madison,  New 


QUATERNARY   BRA. 


407 


Hampshire,  is  estimated  to  weigh  7650  tons.  One  lying 
on  a  naked  ledge  in  Whitingham,  Vermont,  measures  43 
feet  in  length  and  80  in  height  and  width,  or  39,000  cubic 
feet  in  bulk,  and  was  probably  transported  across  Deer- 
field  valley,  the  bottom  of  which  is  500  feet  below  the  spot 
where  it  lies.  Many  on  Cape  Cod  are  20  feet  in  diameter. 
There  are  many  great  bowlders  of  trap  from  50  to  1250 
tons  in  weight  along  the  western  border  of  the  Triassic  area 
in  Connecticut,  the  line  reaching  to  Long  Island  Sound, 
just  west  of  New  Haven  ;  and  others  of  great  magnitude 
occur  farther  south  on  Long  Island.  A  bowlder  in  Ohio, 


FIG.  455. 


Drift  groovings  and  scratches. 

16  feet  in  thickness,  is  said  to  cover  three  fourths  of  an 
acre. 

The  directions  of  travel,  as  learned  by  tracing  the 
stones  in  numerous  cases  to  the  ledges  whence  they  were 
derived,  are,  in  general,  between  southwestward  and  south- 
eastward. The  distance  to  which  the  stones  were  trans- 
ported in  North  America  is  mostly  from  10  miles  or  less 
to  40  miles,  though  in  some  cases  as  much  as  500  miles. 
The  material  was  carried  southward  across  the  depres- 
sions now  occupied  by  the  Great  Lakes  and  Long  Island 
Sound  — the  land  to  the  south,  in  each  case,  being  covered 
with  stones  from  the  land  to  the  north. 


408  HISTORICAL  GEOLOGY. 

Scratches.  —  The  rocky  ledges  over  which  the  drift  was 
borne  are  often  scratched,  in  closely  crowded  parallel 
lines,  as  in  the  preceding  figure  (Fig.  455),  and  planed  off 
besides.  Besides  fine  scratches,  there  are  sometimes  deep 
and  broad  grooves  —  at  times  a  yard  or  more  deep  and 
several  feet  wide,  as  if  made  by  a  tool  of  great  size  as  well 
as  great  power.  The  scratches  occur  wherever  the  drift 
occurs,  provided  the  underlying  rocks  are  sufficiently 
durable  to  have  preserved  them,  and  they  are  usually 
approximately  uniform  in  direction  in  any  given  region. 
In  some  places  two  or  more  directions  may  be  observed  on 
the  same  surface.  They  are  found  in  the  valleys,  and  on 
the  slopes  of  mountains,  to  a  height,  on  the  Green  Moun- 
tains, of  4400  feet,  and,  on  the  White  Mountains,  of  5500 
feet.  They  have  nearly  a  common  course  over  the  higher 
lands  of  a  region,  and  cross  slopes  and  sometimes  even  the 
smaller  valleys,  without  following  the  direction  of  the 
slope  or  valley  ;  but,  in  the  great  valleys  of  the  land,  and 
sometimes  even  in  the  smaller  ones,  their  direction  con- 
forms to  the  trend  of  the  valley.  In  the  Hudson  River 
valley,  between  the  Catskills  and  the  Green  Mountains, 
the  scratches  have  mostly  the  course  of  the  valley ;  and 
also  in  the  valleys  of  the  Connecticut,  the  Merrimac,  and 
other  large  rivers. 

The  stones,  or  bowlders,  of  the  till  are  often  scratched, 
as  well  as  the  underlying  rocks,  and  in  this  respect  they 
differ  from  those  of  stratified  drift ;  the  latter  have  gen- 
erally lost  all  scratches  by  river  abrasion. 

Origin  of  the  Drift.  —  The  earliest  theory  of  the  Drift 
attributed  its  transportation  to  the  tumultuous  waves  of 
a  deluge  sweeping  over  the  land  ;  and  the  formation  was 
formerly  called  Diluvium,  in  allusion  to  this  theory.  Later 
it  came  to  be  generally  admitted  that  nothing  but  moving 
ice  could  have  transported  the  Drift  with  its  immense 
bowlders. 

When  the  inadequacy  of  water  alone  for  the  work  was 
recognized,  the  agency  first  thought  of  was  that  of  float- 


QUATERNARY   ERA.  409 

ing  ice  in  the  form  of  icebergs.  Icebergs  transport  earth 
and  stones,  as  in  the  Arctic  seas ;  and  great  numbers  are 
annually  floated  south  to  the  Newfoundland  Banks,  through 
the  action  of  the  Arctic,  or  Labrador,  current,  where  they 
melt  and  drop  their  great  bowlders  and  burden  of  gravel 
and  earth  to  make  deposits  over  the  sea  bottom.  But  ice- 
bergs could  not  have  covered  great  surfaces  so  regularly 
with  scratches.  Again,  there  are  no  marine  relics  in  the 
unstratified  Drift,  to  prove  that  the  continent  was  under 
the  sea  in  the  Glacial  period. 

These  difficulties  ultimately  led  to  the  well-nigh  uni- 
versal abandonment  of  the  theory  of  icebergs,  and  the 
adoption  of  the  glacier  theory  first  proposed  by  Louis 
Agassiz.  Glaciers,  in  the  Alps  and  elsewhere,  are  now 
doing  precisely  such  work  of  transportation  as  is  shown 
by  the  Drift ;  and  stones  of  as  great  size  as  are  contained 
in  the  Drift  have  in  former  times  been  borne  by  a  slowly 
moving  glacier  from  the  vicinity  of  Mont  Blanc,  across  the 
lowlands  of  Switzerland,  to  the  slopes  of  the  Jura  Moun- 
tains, and  left  there  at  a  height  of  over  2000  feet  above  the 
level  of  the  Lake  of  Geneva.  Moreover,  there  are  in  many 
places  deposits  of  bowlder  clay,  made  of  the  earth  formed 
by  trituration  of  stones  against  stones  during  the  moving 
of  the  glacier.  Further,  there  are  scratches  and  grooves, 
of  precisely  the  same  character  as  those  observed  in  Drift 
regions,  on  the  granitic  and  limestone  rocks  of  the  ridges  ; 
and  besides,  the  transported  material  is  left  unstratified 
over  the  land,  wherever  it  is  not  acted  upon  and  dis- 
tributed by  Alpine  torrents. 

There  is  a  seeming  difficulty  in  the  glacier  theory,  from 
the  supposed  want  of  a  sufficient  slope  in  the  surface  to 
produce  movement.  But  a  slope  in  the  under  surface  is 
not  needed,  any  more  than  for  the  flowing  of  pitch. 
Pitch,  deposited  in  continuous  supply  on  any  part  of  a 
horizontal  plane,  would  spread  in  all  directions  around ; 
and  this  it  would  do  even  if,  instead  of  being  horizontal, 
the  surface  beneath  had  an  ascending  slope.  The  slope 


410  HISTORICAL   GEOLOGY. 

of  the  upper  surface  of  a  plastic  or  fluid  substance  deter- 
mines the  direction  and  rate  of  flow,  not  that  of  the  under 
surface.  Hence,  if  ice  were  accumulated  over  a  region  so 
that  the  upper  surface  had  the  requisite  slope,  there  would 
be  motion  in  the  mass  in  the  direction  of  this  slope,  what- 
ever the  bottom  slope  might  be.  At  the  same  time,  the 
slope  of  the  land  at  bottom,  or  the  courses  of  the  valleys, 
would  determine  to  some  extent  the  movement  at  bottom  ; 
just  as  oblique  grooves  in  a  sloping  board,  down  which 
pitch  was  moving,  would  determine  more  or  less  completely 
the  direction  of  the  movement  in  the  grooves. 

The  condition  of  the  Drift  regions  in  the  Glacial  period 
finds  its  best  illustration,  not  in  the  narrow  and  compara- 
tively shallow  glaciers  of  the  Alpine  valleys,  but  in  the 
great  ice  sheets  of  Greenland  and  the  Antarctic.  Green- 
land is  at  the  present  time  a  glaciated  continent,  as  the 
region  of  Canada  and  the  northeastern  part  of  the  United 
States  was  in  the  Glacial  period.  The  ice  in  Greenland 
moves  where  the  slope  of  the  surface  is  less  than  half  a 
degree. 

The  phenomena  connected  with  the  northern  Drift  are 
in  general  fully  explained  by  reference  to  a  great  northern 
semi-continental  glacier  as  the  cause ;  and  those  relating 
to  local  Drift  about  high  mountains,  south  of  Drift  lati- 
tudes, by  referring  them  to  local  glaciers.  But  floating  ice 
doubtless  had  some  share  in  the  work.  Icebergs  drifted 
down  the  coast,  and  smaller  ones  descended  rivers,  drop- 
ping their  stones  by  the  way.  On  the  Mississippi,  the 
floating  ice  may  have  reached  the  Gulf  of  Mexico,  and  the 
chilled  waters  may  have  destroyed  much  tropical  life. 

The  occurrence  of  bowlders  near  the  summit  of  Mount 
Washington  in  the  White  Mountains  proves  that  the  alti- 
tude of  the  upper  surface  of  the  ice  in  that  region  was 
6000  or  6500  feet ;  and  hence  that  the  ice  was  not  less 
than  5000  feet  thick  over  that  part  of  northern  New 
England.  Facts  also  show  that  the  surface  height  in 
southwestern  Massachusetts  was  at  least  2800  feet ;  in 


QUATERNARY  ERA.  411 

southern  Connecticut,  1000  feet  or  more ;  in  the  Catskills, 
3000  feet  (Smock). 

Since  the  slopes  of  the  upper  surface  of  a  glacier  deter- 
mine the  general  direction  of  movement,  and  therefore  of 
transportation  and  abrasion,  the  lines  of  scratches  or  of 
drift  are  an  indication  as  to  the  position  of  the  ice  summit. 
The  prevailing  direction  over  the  higher  lands  of  New 
England,  New  York,  and  eastern  Canada  is  southeastward, 
and  that  over  western  Ohio  and  northwestward  to  the 
Saskatchewan,  is  south  westward.  (See  map  on  pages 
412,  413.)  The  lines  consequently  converge  northward, 
toward  the  part  of  the  Canada  watershed  northwest  from 
Montreal,  and  a  region  extending  thence  northeastward 
and  northwestward,  encompassing  the  southern  part  of 
Hudson  Bay ;  and  hence  along  this  course  there  must 
have  been  the  summit  of  a  great  ice  range. 

The  stones  and  earth  transported  by  the  continental 
glacier  were  gathered  up  mostly  by  its  lower  part,  from 
the  surface  of  hills  or  ridges  that  projected  into  it,  and 
even  from  the  plains  beneath  it.  In  New  England,  where 
there  were  no  peaks  rising  above  the  upper  surface  to  be  a 
source  of  avalanches,  as  in  the  Alps,  many  of  the  masses 
thus  taken  aboard  exceed  1000  tons  in  weight.  The  mass 
of  decomposed  and  disintegrated  rock  which  had  been 
accumulating  for  ages,  was  extensively  scraped  up  and 
shoved  along.  Even  the  underlying  unaltered  rock  was 
more  or  less  attacked. 

With  a  thickness  of  even  2000  feet,  the  glacier  would 
have  had  great  excavating  power.  Soft  rocks  would  have 
been  deeply  plowed  up  by  it,  and  all  jointed  and  fissile 
rocks,  soft  or  hard,  would  have  been  torn  to  fragments, 
and  the  loosened  masses  borne  off.  ,By  this  means,  and 
perhaps  most  of  all  by  the  erosive  action  of  subglacial 
streams,  valleys  were  deepened  and  widened. 

Area  of  the  Drift  in  North  America. — As  already  stated, 
the  ice  sheet  which  formed  the  Drift  of  Canada  and 
the  northeastern  United  States,  had  its  center  over  the 


Fio.  456. 


412 


FIG.  456. 


MAP  OF 

AMERICA 

ILLUSTRATING  THE  PHENOMENA 

OF  THE 

GLACIAL  AND  CHAMPLAIN 
PERIODS 

Limit  of  ice  sheet  •     - 

Moraines  *• 

n  direction  of  Glacial  \\\\ 


scratches 

Former  shore  line  of  lakes 

75  70 


414  HISTORICAL   GEOLOGY. 

highlands  which  form  the  watershed  between  the  St. 
Lawrence  basin  and  Hudson  Bay.  The  extent  of  the 
Drift  area  (and  consequently  the  maximum  extension  of 
the  ice  sheet)  is  indicated  by  the  heavy  line  on  the  map, 
Fig.  456.  South  and  southeast  of  New  England  the  line 
lies  outside  of  the  present  coast  line.  It  may  be  traced  by 
the  accumulations  forming  the  terminal  moraine,  through 
the  islands  of  Nantucket  and  Marthas  Vineyard,  and  near 
the  south  shore  of  Long  Island.  It  extends  westward 
and  northwestward  across  New  Jersey  and  Pennsylvania, 
crosses  the  boundary  of  New  York  in  a  great  northern 
bend,  follows  a  general  southwesterly  course  through 
western  Pennsylvania,  Ohio  (crossing  once  into  Ken- 
tucky), Indiana,  and  reaches  in  southern  Illinois  the 
lowest  latitude  which  it  anywhere  attains  (below  38°). 
Thence  it  extends  nearly  westward  through  Missouri  into 
eastern  Kansas,  where  it  bends  sharply  northward.  Near 
the  western  boundary  of  North  Dakota  it  passes  above  the 
parallel  of  47°.  Thence  the  line  continues  nearly  west- 
ward across  Montana  till  it  reaches  the  independent  area 
of  Drift  formed  by  the  ice  sheet  of  the  northern  Rocky 
Mountains.  The  contrasted  meteorological  conditions  of 
eastern  and  western  North  America  explain  in  the  main 
the  form  of  the  southern  boundary  of  the  Drift.  In  the 
east,  where  the  precipitation  is  great,  the  boundary  lies 
near  the  parallel  of  40°.  In  the  arid  west,  the  boundary 
recedes  far  to  the  north.  Various  local  conditions,  chiefly 
topographical,  serve  to  explain  the  minor  curves  of  the 
boundary,  as  also  the  occurrence  of  two  isolated  driftless 
areas  within  the  drift  region,  one  of  which  (much  the 
larger  of  the  two),  lying  mostly  within  the  state  of  Wis- 
consin, is  represented  on  the  map. 

Besides  the  great  area  of  the  northeastern  (Laurentide) 
ice  sheet,  glacial  areas  were  developed  in  various  parts  of 
the  Rocky  Mountain  region.  In  the  extreme  northwest 
of  the  United  States  and  in  British  Columbia,  a  large 
area  of  the  northern  Rockies  was  covered  with  a  great  ice 


QUATERNARY   EKA.  415 

sheet,  whose  eastern  edge  met  the  western  edge  of  the 
Laurentide  ice  sheet.  The  boundary  between  the  two  is 
represented  by  a  dotted  line  on  the  map.  The  ice  sheet 
of  the  Rocky  Mountains  in  British  Columbia  had  a 
northern,  as  well  as  a  southern,  limit,  since,  although  the 
cold  increased  northward,  precipitation  decreased.  The 
extreme  northwest  of  British  America,  and  Alaska  (with 
the  exception  of  its  high  mountain  areas),  were  left  un- 
covered by  ice. 

Farther  south,  local  areas  of  glaciation  were  developed 
in  some  of  the  higher  parts  of  the  Rocky  Mountain  region, 
as  in  the  Yellowstone  Park  and  the  mountain  ranges  sur- 
rounding it,  in  the  Front  Range  of  Colorado,  and  in  the 
high  Sierra  of  California. 

It  thus  appears  that  the  glaciation  of  North  America 
was  not  due,  as  has  been  sometimes  imagined,  to  a  great 
polar  ice  cap  investing  all  the  region  of  high  latitude. 
The  centers  of  glaciation  were  in  the  Laurentide  high- 
lands (whose  altitude  was  probably  considerably  greater 
than  now)  and  in  the  Rocky  Mountains.  The  general 
laws  of  the  relation  of  accumulation  of  perpetual  snow  to 
climate  and  topography  were  the  same  as  now.  A  study 
of  glaciation  in  the  Old  World  sustains  the  same  general 
conclusions. 

Subdivisions  of  the  Glacial  Period.  —  The  study  of 
every  glacier  region  reveals  the  fact  of  oscillation  in  the 
extent  of  the  glaciers,  dependent  upon  meteorological  fluc- 
tuations from  year  to  year.  There  were  on  a  larger  scale 
oscillations  in  the  extent  of  the  great  ice  sheets  of  the 
Glacial  period,  though  the  causes  of  these  oscillations  are 
by  no  means  fully  understood. 

The  Glacial  period  in  North  America  may  be  conven- 
iently divided  into  three  epochs,  —  (1)  the  Early  Glacial 
epoch,  or  that  of  the  advance  and  maximum  extension  of 
the  ice ;  (2)  the  Middle  Grlacial  epoch,  or  that  of  the  first 
retreat  of  the  ice ;  (3)  the  Later  G-lacial  epoch,  or  that  of 
the  final  retreat. 


416  HISTORICAL  GEOLOGY. 

The  map  (Fig.  456)  shows  a  well-defined  line  of  ter- 
minal moraine  (BBB),  which  .can  be  traced  in  substan- 
tial continuity  from  Cape  Cod  to  the  Saskatchewan  River. 
In  the  east,  from  Cape  Cod  to  central  Ohio,  that  moraine 
lies  only  a  few  miles  north  of  the  extreme  boundary  of  the 
Drift.  Farther  west,  the  line  of  the  moraine  diverges 
from  the  southern  boundary  of  the  Drift,  and  in  Wiscon- 
sin and  Minnesota  it  sweeps  around  the  driftless  area,  so 
as  to  be  more  than  500  miles  north  of  the  Drift  boundary. 
In  British  America,  in  the  valley  of  the  Saskatchewan, 
the  line  of  the  moraine  lies  300  miles  east  of  the  boundary 
between  the  Laurentide  Drift  and  the  Rocky  Mountain 
Drift. 

The  line  of  moraine  (BBB)  marks  the  limit  of  the 
ice  sheet  in  Middle  Glacial  time,  and  the  distance  between 
the  moraine  and  the  southern  boundary  of  the  Drift  meas- 
ures the  extent  of  the  first  retreat  of  the  ice.  It  is, 
indeed,  possible  that  the  ice  may  have  receded  beyond  the 
line  of  the  moraine  for  a  greater  or  less  distance,  and  then 
readvanced  to  the  line  of  the  moraine.  It  is  held  by 
Chamberlin  and  others  that  the  ice  had  receded  so  far  to 
the  north  as  to  lay  bare  the  greater  part  of  the  territory 
it  had  previously  covered,  thus  characterizing  an  Inter- 
glacial  epoch  between  an  earlier  and  a  later  Glacial  epoch. 
But  it  is  more  probable  that  the  various  terminal  moraines 
mark  halts  in  the  retreat,  or  oscillations,  more  or  less  ex- 
tensive, in  the  position  of  the  ice  front,  than  that  the 
glacial  conditions  were  completely  interrupted  by  one  or 
more  than  one  Interglacial  epoch. 

During  the  rapid  melting  of  the  ice  which  characterized 
the  first  retreat  of  the  glacier,  the  Mississippi  must  have 
been  greatly  swollen,  and  must  have  carried  some  floating 
ice.  To  this  epoch  may  perhaps  be  referred  the  coarse, 
gravelly  deposits  of  the  lower  Mississippi  valley,  with 
flow-and-plunge  structure  and  other  indications  of  torren- 
tial conditions,  and  occasionally  containing  stones  weigh- 
ing 100  pounds  or  more,  described  by  Hilgard  under  the 


QUATERNARY   ERA.  417 

name  of  Orange  Sand,  and  now  included  in  the  Lafayette 
formation  of  McGee  and  others.  By  some  geologists, 
however,  the  Lafayette  formation  is  believed  to  be  of 
Pliocene  age. 

After  a  long  halt  at  the  line  BBB,  the  glacier  con- 
tinued its  retreat.  Numerous  terminal  moraines  mark 
halts  in  the  retreat  or  temporary  readvances.  Some  of 
these  moraines  are  indicated  on  the  map. 

By  the  retreat  of  the  glacier,  the  surface  of  the  country 
was  left  covered  with  Drift,  and  diversified  by  kettle  holes, 
drumlins,  eskers,  and  kames. 

Kettle  holes  are  bowl-shaped  depressions,  often  30  to  50 
feet  in  depth,  and  100  to  500  feet  in  diameter,  sometimes 
even  considerably  exceeding  these  dimensions.  Each 
kettle  hole  was  the  resting  place  and  often  the  burial 
place  of  a  block  of  ice  that  became  detached  from  the 
glacier  during  the  melting,  and  the  final  melting  of  the 
ice  block  left  a  hole  in  the  mass  of  the  Drift  deposits. 
Kettle  holes  are  often  occupied  by  ponds. 

Drumlins  are  elliptical  domes,  consisting  wholly  or  in 
part  of  till. 

Eskers  and  kames  are  ridges  and  hummocks  of  coarsely 
stratified  Drift,  and  are  attributed  to  the  action  of  waters 
flowing  in  or  under  the  wasting  ice. 

By  the  deposit  of  Drift  over  the  region  forsaken  by  the 
ice,  river  valleys  were  often  obstructed,  and  the  streams 
compelled  to  seek  new  channels.  Many  lakes  wer3  formed 
in  valleys  obstructed  by  dams  of  Drift,  or  in  depressions 
left  in  the  irregular  distribution  of  Drift  over  the  country. 
Some  small  lakes,  moreover,  were  formed  in  rock  basins 
excavated  by  the  glacier.  The  glaciated  regions  in  general 
are  regions  abounding  in  lakes. 

The  Glacial  Period  in  Other  Countries.  —  The  main 
facts  in  regard  to  the  Glacial  period  are  the  same  in 
northern  Europe  as  in  North  America.  The  till  presents 
the  same  characteristics,  and  the  bed  rocks  show  the  same 
polished  and  striated  surfaces. 


418  HISTORICAL  GEOLOGY. 

The  center  of  glaciation  for  northern  Europe  was  in 
the  Scandinavian  Mountains.  At  its  period  of  greatest 
extension,  the  ice  sheet  covered  Ireland,  Great  Britain 
(with  the  exception  of  a  little  strip  in  the  extreme  south 
of  England),  Holland,  Denmark,  northern  Germany,  and 
western  Russia  (extending  southward  almost  to  the  Car- 
pathians). In  the  extreme  northeast,  the  Scandinavian 
ice  sheet  became  confluent  with  the  ice  of  the  Timan 
Mountains  and  of  the  northern  part  of  the  Urals,  as  in 
British  Columbia  the  Laurentide  ice  sheet  blended  with 
that  of  the  Rocky  Mountains.  The  fact  that  the  southern 
limit  of  the  Drift  in  Europe  is  about  10°  north  of  that  in 
North  America  suggests  that  there  was  probably  in  the 
Glacial  period  about  the  same  northward  bending  of  the 
isotherms  in  crossing  the  Atlantic  eastward  as  at  present. 
In  the  retreat  of  the  Scandinavian  ice  sheet,  as  in  that 
of  the  Laurentide,  halts  or  temporary  readvances  were 
marked  by  successive  terminal  moraines.  In  the  opinion 
of  many  geologists,  some  of  the  oscillations  were  so  exten- 
sive as  to  characterize  Interglacial  epochs. 

Glaciers  were  developed  on  a  large  scale  in  mountain 
regions  beyond  the  limits  of  the  Scandinavian  ice  sheet. 
After  that  had  retired  from  Great  Britain,  local  glaciers 
were  extensively  developed  in  the  Highlands  of  Scotland. 
The  Alps  formed  the  center  of  an  ice  sheet,  which  extended 
westward  to  Lyons  and  northward  to  the  vicinity  of 
Munich.  Bowlders  from  the  Alps  are  found  in  abundance 
on  the  Jura.  The  glaciers  of  the  Pyrenees,  the  Caucasus, 
and  the  Himalayas  also  extended  far  beyond  their  present 
limits. 

In  South  America,  a  great  ice  mass  extended  in  the  region 
of  the  Andes  northward  from  Tierra  del  Fuego  to  the  par- 
allel of  37°,  and  glaciers  were  formed  about  some  of  the 
higher  summits,  even  near  the  equator.  There  is  evidence 
also  of  a  Glacial  period  in  Australia  and  New  Zealand. 

Cause  of  the  Glacial  Climate.  —  No  perfectly  satisfactory 
explanation  of  the  Glacial  climate  has  been  given.  The 


QUATERNARY   ERA.  419 

upward  movements  of  the  continents  which  characterized 
the  latter  part  of  the  Tertiary,  continued  in  some  regions 
into  the  Quaternary ;  and  in  early  Quaternary  time  large 
areas  in  high  latitudes  stood  at  a  much  higher  level  than 
now.  This  elevation  of  high-latitude  regions  would  tend 
to  bring  on  a  cold  climate,  partly  by  the  direct  effect  of 
elevation  of  land,  and  partly  by  the  exclusion  of  warm 
oceanic  currents  from  the  northern  seas  (see  page  168). 
This  is  an  obvious  and  perhaps  a  sufficient  explanation  of 
the  Glacial  climate.  The  fact  that  the  oscillations  of  level 
and  those  of  climate  seem  not  to  have  been  strictly  simul- 
taneous, is  perhaps  sufficiently  explained  by  the  suggestion 
of  Le  Conte  that  the  accumulation  and  the  removal  of  the 
ice  sheet  were  gradual  processes,  and  that  the  maximum 
effect  might  well  be  considerably  later  than  the  maximum 
intensity  of  the  cause. 

The  former  elevation  of  the  glaciated  regions  is  shown 
by  the  fact  that  their  coasts  are  everywhere  indented  by 
fiords  —  deep,  narrow  bays  penetrating  far  into  the  interior. 
These  fiords  are  unquestionably  drowned  valleys,  and  they 
could  have  been  excavated  only  when  the  land  stood  at  a 
higher  level  than  at  present.  They  are  shown  by  any 
map  on  a  tolerably  large  scale  along  the  coasts  of  Maine, 
Labrador,  Newfoundland,  Greenland,  British  Columbia 
and  Alaska,  Scotland  and  Scandinavia,  Patagonia,  and 
South  Australia.  Some  of  the  fiords  of  the  Atlantic  coast 
of  North  America  have  been  shown  by  soundings  to  have 
depths  of  2000  to  3670  feet,  and  the  Sogne  Fiord  in 
Norway  is  4020  feet  deep.  These  fiords  are  accordingly 
proof  that  some  parts  of  the  land  were  once  thousands  of 
feet  above  their  present  level. 

Valleys  filled  with  drift,  deeper  than  the  present  river 
valleys  in  the  same  regions,  and  often  extending  far  below 
the  level  of  the  sea,  afford  other  evidence  of  the  former 
high  level  of  the  land. 

The  Glacial  climate  has  been  attributed  by  Croll  and 
many  other  geologists  to  the  extreme  cold  of  aphelion 


420  HISTORICAL  GEOLOGY. 

winters  in  an  epoch  of  maximum  eccentricity  of  the 
earth's  orbit.  The  theory  has  been  briefly  explained  on 
page  169.  It  is  very  doubtful  whether  the  astronomical 
conditions  assumed  by  Croll  would  tend  to  produce  'a 
Glacial  period.  The  great  heat  of  perihelion  summers 
would  certainly  tend  to  melt  the  snow.  Moreover,  the  last 
period  of  great  eccentricity  ended  about  70,000  years  ago, 
whereas  geological  evidence  indicates  that  the  close  of  the 
Glacial  period  was  much  more  recent.  A  corollary  of  Croll's 
theory  would  be  the  occurrence  of  glacial  and  interglacial 
epochs  in  the  northern  hemisphere,  alternately  with  corre- 
sponding epochs  in  the  southern  hemisphere,  during  a  period 
of  great  eccentricity.  There  is  no  proof  of  such  alternate 
glaciation  of  the  two  hemispheres,  though  it  is  not  im- 
possible. 

2.  CHAMPLAIN  PERIOD. 

This  period  is  so  named  from  the  marine  deposits  around 
the  shores  of  Lake  Champlain. 

The  Champlain  period  is  characterized  by  (1)  the  con- 
tinuance of  the  subsidence  which  had  probably  begun  in 
the  latter  part  of  the  Glacial  period,  the  land  in  northern 
latitudes  becoming  depressed  considerably  below  the  pres- 
ent level ;  (2)  a  diminution  in  the  slope  of  southward-flow- 
ing rivers,  so  that  they  ceased  for  the  most  part  from  the 
work  of  erosion,  and  formed  extensive  stratified  deposits ; 
(3)  a  climate  probably  warmer  than  at  present — doubtless, 
at  least  in  part,  the  result  of  the  subsidence  ;  (4)  the  com- 
plete disappearance  of  the  great  ice  sheets. 

The  deposits  of  the  Champlain  period  are  (1)  marine, 
(2)  fluviatile,  (3)  lacustrine.  In  general,  it  is  only  the 
marine  deposits  which  afford  positive  evidence  and  definite 
measures  of  the  subsidence  ;  since  fluviatile  and  lacustrine 
deposits  may  be  formed  at  various  altitudes  above  the  sea 
level,  the  height  of  the  water  being  modified  by  dams  of 
drift  or  of  ice,  and  by  variations  in  the  ratio  of  precipita- 
tion and  evaporation,  as  well  as  by  changes  in  the  level  of 
the  land. 


QUATERNARY  ERA.  421 

1.  Marine  Deposits;  Sea  Beaches. — Marine  deposits  oc- 
cur as  sea  beaches,  now  forming  terraces  above  the  present 
shore  lines,  or  as  offshore  deposits  —  the  Leda  Clays. 

Along  the  coast  of  southern  New  England,  there  are 
apparently  no  marine  Champlain  deposits  more  than  15  or 
20  feet  above  the  sea  level.  The  fossiliferous  deposits  of 
Sankaty  Head,  Nantucket,  reaching  an  altitude  of  about 
50  feet,  and  those  at  a  still  higher  elevation  at  Gay  Head, 
Marthas  Vineyard,  are  apparently  earlier  than  the  true 
Champlain  deposits.  They  probably  belong  to  some  time 
of  oscillation  when  the  ice  front  had  receded  to  a  greater 
or  less  distance  from  the  limit  to  which  it  subsequently 
readvanced  (page  416).  Marine  deposits  of  Champlain 
age  along  the  coast  of  Maine  occur  at  altitudes  of  150  to 
300  feet.  In  the  basin  of  the  Bay  of  Chaleurs,  the  alti- 
tude is  200  feet.  Along  the  St.  Lawrence  valley,  the 
height  is  375  feet  near  the  mouth  of  the  Saguenay,  520 
feet  at  Montreal,  and  600  feet  not  far  from  Lake  Ontario, 
so  that  the  St.  Lawrence  River  was  then  a  vast  St. 
Lawrence  Gulf,  500  to  600  feet  deep.  Even  Lake  Cham- 
plain  was  an  arm  of  this  St.  Lawrence  Gulf ;  for  beaches 
containing  sea  shells  occur  on  its  borders  to  a  height  of 
370  feet  at  its  southern,  and  about  500  feet  at  its  northern, 
end ;  and  in  one  locality  remains  of  a  Whale  have  been 
found.  The  Champlain  bay  had  then  the  great  depth  of 
from  700  to  800  feet.  At  Nachvak,  in  Labrador,  a  beach 
supposed  to  be  of  Champlain  age  is  reported  at  an  altitude 
of  1500  feet.  In  the  region  south  and  west  of  James  Bay, 
beds  with  marine  shells  occur  at  altitudes  of  300  to  500  feet. 

The  maximum  subsidence  in  eastern  North  America 
seems  to  have  been  in  the  region  between  the  St.  Law- 
rence and  Hudson  Bay  —  the  region  probably  of  maximum 
elevation  in  the  Glacial  period. 

On  the  Pacific  coast,  marine  beaches  are  reported  at 
altitudes  exceeding  1000  feet,  but  it  is  not  known  whether 
they  belong  to  the  same  date  as  the  Champlain  beds  of 
eastern  North  America  or  not. 


422  HISTORICAL   GEOLOGY. 

While  there  is  much  uncertainty  in  regard  to  the  num- 
ber and  extent  of  climatic  and  geographical  oscillations  in 
Europe,  it  appears  certain  that  extensive  subsidence  took 
place  subsequently  to  the  period  of  maximum  glaciation. 
The  subsidence  carried  parts  of  Great  Britain  500  feet 
below  the  present  level.  In  Sweden  the  depression  varied 
from  200  feet  in  the  southern  part  to  more  than  600  in 
the  northern  part.  At  the  time  of  deepest  submergence, 
the  Baltic  is  believed  to  have  been  connected  with  the 
North  Sea  by  the  region  of  lakes  extending  westward 
from  Stockholm  to  the  Skager  Rack,  and  with  the  Arctic 
Ocean  by  a  channel  extending  over  Finland  to  the  White 
Sea. 

2.  Fluvial  Deposits.  —  The  subsidence  of  the  land  north- 
ward diminished  the  slope  of  all  southward-flowing  rivers, 
and  consequently  diminished  their  powers  of  erosion. 
Moreover,  the  enormous  mass  of  debris  which  had  been 
transported  by  the  glaciers,  and  was  set  free  by  their 
melting,  overloaded  the  rivers.  The  effect  of  these  causes 
combined,  was  the  deposit  of  enormous  masses  of  sediment, 
filling  up  the  river  valleys  of  the  glaciated  region  to  a 
height  now  indicated  by  the  highest  terraces.  The  rivers 
meandered  over  these  great  alluvial  plains  (sometimes 
many  miles  in  width),  and  in  time  of  floods  spread  widely 
over  their  surface.  These  alluvial  plains  were  in  fact  the 
flood  plains  of  the  Champlain  rivers. 

The  structure  of  the  deposits  presents  great  variations. 
Some  parts  consist  of  fine  clays,  with  regular  lamination, 
indicating  deposit  in  quiet  waters,  as  of  lakes.  Others 
consist  of  coarse  sands,  gravels,  or  cobble  stones,  and  show 
the  flow-and-plunge  structure  and  other  forms  of  irreg- 
ular lamination,  indicative  of  strong  currents.  In  places 
the  northward  subsidence  must  have  reduced  the  slope  of 
streams  to  zero,  so  that  they  would  spread  out  in  broad 
lakes.  In  other  places  lacustrine  conditions  must  have 
been  produced  by  dams  of  drift  or  ice.  Coarse  materials 
would  often  be  brought  into  the  larger  streams  by  tribu- 


QUATERNARY  ERA.  423 

taries  whose  slope  and  velocity  were  greater  than  those 
of  the  larger  streams,  and  would  be  piled  up  as  deltas  near 
the  mouths  of  those  tributaries.  Rapid  melting  of  the 
ice  during  part  of  the  time  may  have  increased  the  vol- 
ume of  water,  and  so  increased  the  velocity  of  the  streams. 

3.  Lakes  of  the  Pleistocene.  —  Lake  basins  in  various 
parts  of  the  country  are  plainly  marked  by  shore  lines 
formed  in  Pleistocene  time.  In  some  cases  the  basins  are 
still  occupied  by  smaller  lakes,  and  the  old  beaches  appear 
as  terraces  far  above  the  present  shore  lines.  In  other 
cases,  the  lakes  have  been  drained,  so  that  no  considerable 
remnants  now  exist.  Climatic  changes,  and  dams  of  drift 
or  of  ice,  as  well  as  movements  of  subsidence  and  elevation, 
may  have  been  concerned  in  determining  the  existence 
and  the  boundaries  of  these  lakes.  The  correlation  of 
the  history  of  the  lakes  with  the  history  of  general  con- 
tinental movements  indicated  by  fiords  and  by  sea  beaches, 
is  matter  of  much  question. 

Ancient  beaches  have  been  observed  in  many  places 
around  the  Great  Lakes  of  the  Canadian  frontier.  Some 
of  those  which  have  been  most  thoroughly  studied  are 
shown  by  dotted  lines  on  the  map,  Fig.  456.  The  highest 
shore  line  around  Lake  Superior  has  an  altitude  of  500 
to  600  feet  above  the  present  level  of  the  lake,  or  of 
1100  to  1200  feet  above  the  level  of  the  sea.  At  the 
south  end  of  Lake  Michigan,  the  highest  shore  line  is 
only  45  feet  above  the  present  level  of  the  lake.  This 
beach  is  supposed  to  be  contemporaneous  with  one  around 
parts  of  Lake  Superior  about  400  feet  above  the  lake. 
A  very  strongly  marked  shore  line  has  been  traced  around 
the  greater  part  of  Lake  Ontario,  and  has  been  named 
the  Iroquois  beach.  It  has  a  height  above  the  present 
water  level  varying  from  116  feet  near  the  western  end 
of  the  lake  to  483  feet  at  Watertown,  New  York.  The 
great  difference  between  the  altitudes  of  beaches  around 
the  various  lakes  which  have  been  supposed  to  be  con- 
temporaneous, and  especially  the  great  difference  between 


424  HISTORICAL   GEOLOGY. 

the  altitudes  of  different  parts  of  the  same  continuous 
beach  (as  in  the  case  of  the  Iroquois  beach),  is  evidence 
of  great  changes  of  relative  level  in  different  parts  of 
the  lake  region. 

There  seems  good  reason  to  believe  that  at  one  time 
the  four  upper  lakes  were  confluent  into  one  lake,  more 
than  100,000  square  miles  in  area,  which  has  been  named 
Lake  Warren  (in  honor  of  General  Warren,  the  discov- 
erer of  Lake  Agassiz). 

The  high^  level  of  the  water  in  these  Pleistocene  lakes 
has  been  attributed  by  many  geologists  to  the  presence 
of  the  remnant  of  the  continental  ice  sheet  in  the  St.  Law- 
rence valley,  damming  up  the  outlet  in  that  direction, 
and  compelling  the  waters  to  seek  outlets  southward  at 
higher  levels.  Others  hold  that,  at  the  time  of  the  exist- 
ence of  these  lakes,  the  ice  had  already  receded  from  the 
St.  Lawrence  valley,  and  that  the  great  extension  of  the 
lakes  was  due  to  the  Champlain  subsidence.  At  the  time 
of  maximum  Champlain  depression,  the  Iroquois  beach 
must  have  been  very  nearly  at  the  sea  level;  but  the 
absence  of  marine  fossils  shows  that  Lake  Ontario  did 
not  (like  Lake  Champlain)  have  so  free  communication 
with  the  sea  as  to  become  salt.  It  is  supposed  by  many 
geologists  that,  at  the  time  of  the  Iroquois  beach,  Lake 
Ontario  communicated  with  the  sea  by  a  channel  leading 
from  Rome,  New  York,  to  the  Mohawk  valley,  and  thence 
by  way  of  the  Hudson;  but  this  is  not  certain. 

The  region  of  Lake  Winnipeg  was  occupied  at  some 
time  in  the  Pleistocene  by  a  lake  even  larger  than  Lake 
Warren,  which  has  been  named  Lake  Agassiz  (see  map, 
Fig.  456).  General  G.  K.  Warren,  who  first  made  known 
the  fact  of  the  former  drainage  of  the  Winnipeg  region 
into  the  Mississippi  by  way  of  the  Minnesota,  attributed 
the  southward  drainage  to  that  high  elevation  of  the 
northern  part  of  the  continent,  which  existed  at  the 
beginning  of  the  Quaternary.  According  to  this  view, 
the  beginning  of  the  Champlain  subsidence  depressed 


QUATERNARY  EKA.  425 

the  Winnipeg  region  so  greatly  as  to  form  Lake  Agas- 
siz.  The  further  progress  of  subsidence  depressed  the 
region  to  the  north  so  far  that  Lake  Agassiz  found  an 
outlet  through  Nelson  River  into  Hudson  Bay,  and  the 
Red  River  of  the  North  began  to  flow  northward  instead 
of  southward.  According  to  Upham  and  others,  the 
southward  drainage  of  the  Winnipeg  region  was  due 
to  the  presence  of  the  ice  sheet,  damming  up  the  Nelson 
River  outlet.  In  the  case  of  Lake  Agassiz,  as  in  that 
of  Lake  Warren  and  the  other  lakes  of  the  Canadian 
frontier,  there  is  evidence  of  considerable  oscillations  of 
level  in  the  very  different  altitudes  of  different  parts  of 
the  same  beach. 

Lake  Bonneville  is  the  name  of  a  Pleistocene  lake 
occupying  a  large  part  of  Utah,  and  Lake  Lahontan  the 
name  of  one  occupying  a  large  part  of  western  Nevada 
(see  map,  Fig.  456).  The  Great  Salt  Lake  is  the  dimin- 
ished representative  of  the  former,  while  the  latter  is 
now  represented  by  still  smaller  remnants.  At  one  time 
Lake  Bonneville  rose  so  high  as  to  find  an  outlet  through 
the  Snake  River  and  the  Columbia,  and  thus  became  fresh; 
but  Lake  Lahontan  never  had  an  outlet.  The  high  level 
of  the  water  in  these  lakes  is  attributed  to  the  cold 
climate  of  the  Glacial  period,  which  must  have  diminished 
evaporation.  According  to  Gilbert,  King,  and  Russell, 
there  is  evidence  of  two  high-water  stages  in  each  of 
these  lakes,  with  an  intervening  epoch  in  which  the  lakes 
were  nearly  or  quite  desiccated.  It  is  still  uncertain 
what  phases  in  the  Pleistocene  history  of  eastern  North 
America  are  to  be  correlated  with  the  alternations  of 
high  and  low  water  in  these  lakes  of  the  Great  Basin. 

3.  RECENT  PERIOD. 

The  Champlain  period  was  brought  to  a  close  by  a 
moderate  elevation  of  the  land  over  the  higher  latitudes, 
bringing  the  continent  up  to  its  present  level.  This  ele- 
vation placed  the  old  sea  beaches  of  the  Champlain  period 


426 


HISTORICAL  GEOLOGY. 


at  their  present  level,  high  above  the  sea ;  that  is,  over 
500  feet  near  Montreal,  150  to  300  feet  on  the  coast 
of  Maine,  and  so  on,  the  height  of  the  beaches  being 
a  measure  of  the  amount  of  elevation.  River  valleys, 
after  the  rise,  had  a  steeper  slope  than  in  the  Champlain 
period,  and  hence  their  flow  was  increased  in  velocity. 
They  consequently  went  on  cutting  down  their  beds 
through  the  Champlain  deposits  of  the  valley  to  a  lower 
level ;  and  at  the  time  of  their  annual  floods  they  wore 

FIG.  457. 


Terraces  on  the  Connecticut  Kiver,  south  of  Hanover,  New  Hampshire. 

away  the  deposits  on  either  side  of  the  channel,  making 
thereby  an  alluvial  flat  or  flood  ground  ;  for  a  river  has, 
in  general,  a  flood  ground  which  it  covers  in  its  times  of 
flood,  as  well  as  a  channel  for  dry  times. 

This  sinking  of  the  river  beds  left  remnants  of  the 
old  flood  grounds  as  terraces  far  above  the  level  of  the 
stream.  In  the  course  of  the  elevation,  a  series  of  ter- 
races was  often  made  along  the  valleys,  as  illustrated  in 
Fig.  457.  A  section  of  a  valley  thus  terraced  is  repre- 
sented in  Fig.  458.  The  formation  terraced  is,  as  is 


QUATERNARY   ERA.  427 

shown,  the  Champlain  (sometimes  in  part  Glacial  Drift)  ; 
in  the  Champlain  period  it  filled,  in  general,  the  valley 
across  (from  /  to  /'),  excepting  a  narrow  channel  for  the 
stream,  the  whole  breadth  having  been  the  flood  ground 
of  the  Champlain  river.  But,  after  the  elevation  began 
which  closed  the  Champlain  period,  the  river  commenced 
to  cut  down  through  the  formation,  making  one  or  more 
terraces  in  it,  on  either  side  of  the  stream.  In  general, 
each  terrace  below  the  uppermost  one  indicates  a  pause 
in  the  movement  of  elevation,  being  really  a  remnant  of 
a  flood  plain  formed  while  the  river  was  nearly  at  base 
level  (pages  131,  138).  In  Fig.  458,  R  is  the  position  of 
the  river  channel  after  the  terracing ;  and  on  either  side 
of  it  there  are  terraces  at  the  levels  ff,  dr,  bbf,  and  also 

FIG.  458. 


d  , 


Section  of  a  valley  with  terraces. 

another  on  the  right  side,  at  rdf.  These  terrace  plains 
are  usually  the  sites  of  villages.  They  add  greatly  to  the 
beauty  of  the  scenery  along  water  courses.  The  terraces 
usually  fail  where  the  valley  is  narrow  and  rocky: 

In  Europe,  the  close  of  the  period  of  subsidence  (Cham- 
plain)  seems  to  have  been  marked  by  a  recurrence  of 
Glacial  conditions,  the  northern  portions  of  that  continent 
being  again  covered  with  ice,  and  glaciers  extending  once 
more  from  the  Alps  over  part  of  lower  Switzerland. 
Proofs  of  the  occurrence  of  such  an  epoch  are  found  in 
the  remains  of  the  Reindeer  and  other  sub-arctic  animals, 
in  southern  France  (page  437),  in  deposits  that  are  sub- 
sequent in  date  to  true  Champlain  deposits. 

MODERN  CHANGES  OF  LEVEL. 

The  sea,  the  rivers,  the  winds,  and  all  mechanical  and 
chemical  forces  are  still  working  as  they  have  always 


428  HISTORICAL   GEOLOGY. 

worked ;  and  the  earth  is  undergoing  changes  of  level, 
also,  over  wide  areas,  although  it  has  beyond  question 
reached  an  era  of  comparative  repose. 

These  changes  of  level  are  either  paroxysmal  —  that  is, 
they  take  place  through  a  sudden  movement  of  the  earth's 
crust,  as  sometimes  happens  in  connection  with  an  earth- 
quake ;  or  they  are  secular  —  that  is,  they  are  the  effect 
of  a  gradual  movement  prolonged  through  many  years  or 
centuries.  The  following  are  some  examples:  — 

1.  Paroxysmal  Movements.  —  In  1822,  the  coast  of  Chile 
for  1200  miles  was  shaken  by  an  earthquake,  and  it  has 
been  estimated  that  the  coast  near  Valparaiso  was  raised 
at  the  time  3  or  4  feet.     In  1835,  during  another  earth- 
quake in  the  same  region,  there  was  an  elevation,  it  is 
stated,  of  4  or  5  feet  at  Talcahuano,  which  was  reduced 
after  a  few  months  to  2  or  3  feet.     In  1819,  there  was  an 
earthquake  about  the   Delta   of   the    Indus,   and   simul- 
taneously an  area  of  2000  square  miles,'  in  which  the  fort 
and  village  of  Sindree  were  situated,  sunk  so  as  to  become 
an  inland  sea,  with  the  tops  of  the  houses  just  out  of 
water  ;  and  another  region  parallel  with  the  sunken  area, 
50  miles  long  and  in  some  parts  10  miles  broad,  was  raised 
10  feet  above  the  delta.     These  few  examples  all  happened 
within  an  interval  of  sixteen  years.     They  show  that  the 
earth  is  still  far  from  absolute  quiet,  even  in   this  its 
finished  state. 

2.  Secular  Movements.  —  Along  the  coasts  of   Sweden 
and  Finland,  on  the  Baltic,  there  is  evidence  that  a  gradual 
rising  of   the  land  is  in  slow  progress.      Marks  placed 
along  the  rocks  many  years  since  show  that  the  change 
is  slight  at  Stockholm,  but  increases  northward.     Evi- 
dence of  elevation  has  been  obtained  from  the  west  coast 
as  well  as  from  the  east  coast,  showing  that  the  apparent 
elevation  is  not  due  to  oscillations  in  the  water  level  of 
the  Baltic.     At  Udde valla  the  rate  of  elevation  is  equiva- 
lent to  3  or  4  feet  in  a  century. 

In   Greenland,  for   600-  miles,  from   Disco   Bay,  near 


QUATERNARY   ERA.  429 

69°  N.,  to  the  frith  of  Igaliko,  60°  43'  N.,  a  slow  sinking 
has  been  going  on  for  at  least  four  centuries.  Islands 
along  the  coast,  and  old  buildings,  have  been  submerged. 
The  Moravian  settlers  have  had  to  put  down  new  poles 
for  their  boats,  and  the  old  ones  stand  "as  silent  witnesses 
of  the  change." 

It  is  believed  also  that  a  sinking  is  in  progress  along 
the  coast  of  New  Jersey,  Long  Island,  and  Marthas  Vine- 
yard, and  a  rising  in  different  parts  of  the  coast  region 
between  Labrador  and  the  Bay  of  Fundy.  There  are 
deeply  buried  stumps  of  forest  trees  along  the  seashore 
plains  of  New  Jersey,  and  other  evidences  of  a  change  of 
level  (G.  H.  Cook). 

This  fact  is  to  be  noted,  that  these  secular  movements 
of  modern  time  over  the  continents  are,  for  the  most  part, 
so  far  as  observed,  high-latitude  oscillations,  just  as  they 
were  in  the  earlier  part  of  the  Quaternary. 

Life  of  the  Quaternary. 

The  history  of  Quaternary  life  is  remarkable  for  the 
extensive  migrations  occasioned  by  the  great  geographical 
and  climatic  changes  of  the  era.  With  the  increasing  cold 
of  the  Glacial  period,  the  range  of  various  species  of  plants 
and  animals  was  contracted  on  the  north  and  extended  to 
the  south.  With  the  coming  on  of  the  mild  climate  of  the 
Champlain,  there  was  a  corresponding  northward  shifting 
of  the  range  of  various  species.  In  the  northward  migra- 
tion, colonies  of  northern  plants  and  animals  were  left  in 
regions  of  high  mountains,  far  south  of  their  normal  range, 
finding  on  those  summits  a  congenial  climate,  and  freedom 
from  competition  with  the  southern  flora  and  fauna  of  the 
low  grounds.  Plants  and  Insects  of  Labrador  and  the  far 
north  occur  on  the  summits  of  the  White  Mountains,  the 
Green  Mountains,  and  the  Adirondacks.  Analogous  facts 
are  reported  from  the  Alps  and  other  mountain  regions 
of  Europe.  The  distribution  of  the  flora  and  fauna  was 


430  HISTORICAL   GEOLOGY. 

affected  by  all  the  minor  oscillations  of  climate,  the  more 
hardy  plants  and  animals  crowding  upon  the  edge  of  the 
ice  sheet,  and  moving  northward  with  every  recession  of 
the  front  of  the  ice.  While  many  species  only  migrated 
southward  and  northward  with  the  advance  and  recession 
of  the  ice,  other  species  were -exterminated  by  the  climatic 
changes. 

The  elevation  of  land  in  part  of  Quaternary  time  estab- 
lished land  connection  between  the  eastern  and  the  western 
continent  by  way  of  the  region  of  Bering  Strait,  perhaps 
also  by  way  of  the  Faroe  Islands,  Iceland,  and  Greenland. 
The  British  Islands  were  connected  with  the  continent  of 
Europe,  and  Europe  was  connected  with  Africa  across  the 
Mediterranean.  More  or  less  of  migration  took  place  in 
all  these  cases  between  the  areas  thus  connected. 

The  Invertebrate  animals  of  the  Quaternary,  and  proba- 
bly also  the  plants,  were  very  nearly  if  not  quite  all  identi- 
cal with  existing  species.  The  shells  and  other  Invertebrate 
remains  found  in  the  beds  on  the  St.  Lawrence,  Lake  Cham- 
plain,  and  the  coast  of  Maine,  are  similar  to  those  now 
found  on  the  coast  of  Maine  or  Labrador,  or  farther  north. 

The  life  of  the  Quaternary  of  greatest  interest  is  the  Mam- 
malian, which  type,  as  regards  brutes,  culminated  in  the 
Champlain  period.  This  culmination  was  manifested  in 
—  (1)  the  number  of  species,  (2)  the  magnitude  of  the 
animals  —  the  Mammalian  life  of  the  period  exceeding  in 
each  of  these  particulars  that  of  the  present  time. 

Along  with  the  brute  Mammals  of  the  Quaternary  ap- 
peared also  Man. 

BRUTE  MAMMALS. 

Europe  and  Asia.  —  The  bones  of  Mammals  are  found 
in  caves  that  were  their  old  haunts ;  in  stratified  deposits 
along  rivers  and  lakes ;  in  sea-border  deposits ;  in  marshes, 
where  the  animals  were  mired;  in  ice,  where  they  have 
been  preserved  from  decay  by  the  intense  cold. 

The  caves  on  the  continent  of  Europe  were  the  resort 


QUATERNARY   ERA.  431 

especially  of  the  Cave  Bear  (Ursus  spelceus),  and  those  of 
Great  Britain  of  the  Cave  Hyena  (Jlycena  spelcea).  Into 
their  dens  they  dragged  the  carcasses  or  bones  of  other 
animals  for  food,  so  that  relics  of  a  large  number  of  species 
are  now  mingled  together  in  the  earth  or  stalagmite  which 
forms  the  floor  of  the  cavern.  In  a  cave  at  Kirkdale, 
England,  portions  of  a  very  large  number  of  Hyenas  have 
been  made  out,  besides  remains  of  an  Elephant,  Lion,  Bear, 
Wolf,  Fox,  Hare,  Weasel,  Rhinoceros,  Horse,  Hippopota- 
mus, Ox,  Deerv  and  other  species,  all  then  inhabitants  of 
that  country.  A  cave  at  Gaylenreuth  is  said  to  have 
afforded  fragments  of  at  least  800  individuals  of  the  Cave 
Bear.  The  Cave  Hyena  is  regarded  as  a  large  variety  of 
the  HycBna  crocuta  of  South  Africa,  and  the  Cave  Lion,  a 
variety  of  Felis  leo,  the  Lion  of  Africa.  But  many  of  the 
Quaternary  species  are  now  extinct. 

The  fact  that  the  number  of  species  in  the  Quaternary 
was  greater  than  now,  may  be  inferred  from  a  comparison 
of  the  fauna  of  Quaternary  Great  Britain  with  that  of 
any  region  of  equal  area  in  the  present  age.  The  species 
included  gigantic  Elephants,  two  species  of  Rhinoceros,  a 
Hippopotamus,  three  species  of  Oxen,  two  of  them  of 
colossal  size,  several  species  of  Deer,  including  the  colossal 
Irish  Deer  (Cervus  euryceros),  whose  height  to  the  sum- 
mit of  its  antlers  was  10  to  11  feet,  and  the  span  of  whose 
antlers  was  in  some  cases  12  feet,  the  Horse,  Ass,  Wild 
Boar,  Wildcat,  Lynx,  Leopard,  Lion,  the  huge  Saber- 
toothed  Tiger  (Machcerodus),  with  canines  sometimes 
eight  inches  long,  the  Cave  Hyena,  and  Cave  Bear, 
besides  various  smaller  species. 

The  Mammoth  (Elephas  primigenius)  was  nearly  a 
third  taller  than  the  largest  modern  species  of  Elephant. 
It  roamed  over  Great  Britain,  middle  and  northern  Europe, 
northern  Asia,  even  to  its  Arctic  shores,  and  North 
America.  Great  quantities  of  tusks  have  been  exported 
from  the  borders  of  the  Arctic  Sea  for  ivory.  These  tusks 
sometimes  have  a  length  of  12|-  feet.  Near  the  beginning 


432  HISTORICAL  GEOLOGY. 

of  the  century  one  of  these  Elephants  was  found  frozen  in 
ice  at  the  mouth  of  the  Lena ;  and  it  was  so  well  pre- 
served that  wolves  and  bears  ate  of  the  ancient  flesh.  Its 
length  to  the  extremity  of  the  tail  was  16J  feet,  and  its 
height  9J  feet.  It  had  a  coat  of  long  hair.  But  no 
amount  of  hair  would  enable  an  Elephant  now  to  live  in 
those  barren,  icy  regions,  where  the  mean  temperature 

FIG.  459. 


PROBOSCIDEAN  :  Mastodon  giganteus. 

in  winter  is  40°  F.  below  zero.  Siberia  had  also  a  hairy 
Rhinoceros. 

Although  there  were  many  Ungulates  among  the  Qua- 
ternary species  of  the  Orient,  the  most  characteristic 
animals  were  the  great  Carnivores. 

North  America.  - —  In  the  Champlain  period,  there  were 
great  Elephants  and  Mastodons,  Oxen,  Horses,  Stags, 
Beavers,  and  some  Edentates,  in  North  America,  unsur- 
passed in  magnitude  by  any  in  other  parts  of  the  world. 


QUATERNARY   ERA.  "433 

Ungulates  were  the  characteristic  type.  Of  Carnivores 
there  were  comparatively  few  species ;  no  true  cavern 
species  have  been  discovered.  Fig.  459  (from  Owen) 
represents  the  specimen  of  the  American  Mastodon  now 
in  the  British  Museum.  The  skeleton  set  up  by  Dr. 
Warren  in  Boston  has  a  height  of  11  feet,  and  a  length, 
to  the  base  of  the  tail,  of  17  feet.  It  was  found  in  a 
marsh  near  Newburgh,  New  York.  The  Mammoth  (Ele- 
phas  primigenius}  was  the  most  common  and  wide-ranging 
species  of  Elephant  in  North  America,  as  in  Europe  and 
Asia. 

.  460. 


EDENTATE:  Megatherium  Cuvieri  (x  ^). 

South  America.  —  South  America  had,  at  the  same 
time,  its  Carnivores  and  Ungulates  ;  but  it  was  most 
remarkable  for  its  Edentates,  or  animals  related  to  the 
Sloths  and  Armadillos. 

Fig.  460  shows  the  form  and  skeleton  of  one  of  these 
animals  —  the  Megatherium.  It  exceeded  in  size  the  largest 
Rhinoceros :  a  skeleton  in  the  British  Museum  is  18  feet 
long.  It  was  a  clumsy,  slothlike  beast,  but  exceeded 
immensely  the  modern  Sloths  in  size.  Another  group  of 
Edentates,  related  to  the  modern  Armadillos,  had  an 
armor  of  bony  plates  developed  in  the  skin,  giving  them 
a  superficial  resemblance  to  Turtles.  One  genus  named 


434  HISTORICAL   GEOLOGY. 

G-lyptodon  is  represented  in  Fig.  461,  though  it  has  been 
recently  discovered  that  the  tail  shown  in  the  figure 
belongs  to  another  genus.  Many  of  the  animals  of  this 
group  also  were  gigantic,  the  Glyptodon  here  figured 
having  had  a  shell  or  carapace  five  or  six  feet  in  length. 

South  America  was  eminently  the  continent  of  Eden- 
tates. 

Australia. — The  Mammals  of  Australia,  in  the  Cham- 
plain  period,  were  almost  exclusively  Marsupials,  as  is 
the  case  in  modern  Australia ;  but  these  partook  of  the 
gigantic  size  so  characteristic  of  the  Mammalian  life  of 
the  period.  The  genus  Diprotodon  was  as  large  as  a 
Hippopotamus,  and  Nototherium  was  as  large  as  an  Ox. 

FIG.  461. 


EDENTATE:  Glyptodon  clavipes  (x 


Conclusions.  —  The    facts    sustain    the   following   con- 
clusions :  — 

1.  The  Champlain  period  of  the  Quaternary  was  the 
time  of  culmination  of  Mammals,  both  as  to  numbers  and 
as  to  magnitude. 

2.  The   Mammalian   faunas  of  the  various  continents 
showed  the  same  ordinal  types  by  which  they  are  now 
characterized,  but  many  of  the  species  were  much  larger 
than    now    exist.       Thus,    the    Orient   had    its    gigantic 
Carnivores  ;   South  America  its  gigantic  Edentates  ;  Aus- 
tralia its  gigantic  Marsupials. 

3.  The  climate   of  Great   Britain   and   the   continent 


QUATERNARY   ERA.  435 

of  Europe,  where  were  the  haunts  of  Lions,  Tigers, 
Hippopotamuses,  etc.,  must  have  been  warmer  than  now, 
and  probably  not  colder  than  warm-temperate.  The 
climate  of  Arctic  Siberia  was  such  that  shrubs  could 
have  grown  there  to  feed  the  herds  of  Elephants,  and 
hence  could  not  have  been  below  sub-frigid,  for  which 
degree  of  cold  it  is  possible  the  animals  might  have 
been  adapted  by  their  hairy  covering. 

4.  The   Champlain  period,  the  meridian  time   of  the 
Quaternary  Mammals,  was,  accordingly,  as  before  stated, 
one  of  warmer  climate  over  the  northern  continents  than 
the  present,  and  much  warmer  than  that  of  the  Glacial 
period.     The  species  may  have  begun  to  exist  before  the 
Glacial  period  ended  ;    but  they  belonged  preeminently 
to  the  Champlain  period. 

5.  The   larger   part   of    the    great    Mammals    of   the 
Quaternary  disappeared  with  the  close  of  the  Champlain 
period  or  in  the  early  part  of  the  Recent  period,  while 
others  found  refuge  in  the  tropics.     They  were  animals 
of  a  warmer  climate  than  now  belongs  to  the   regions 
which  they  then  inhabited;    and  the  change  to  a  some- 
what colder  climate  at  the  close  of  the  Champlain  period 
probably   brought   about   the   extermination   and   forced 
migration. 

Although  there  is  no  evidence  in  North  America  of  a 
recurrence  of  Glacial  conditions  after  the  Champlain 
period,  it  is  probable  that  there  may  have  been  oscilla- 
tions of  climate  analogous  to  those  of  Europe,  the  climate 
just  at  the  close  of  the  Champlain  period  being  somewhat 
colder  than  at  present.  Such  an  oscillation  of  climate 
is  perhaps  indicated  by  remains  of  Reindeer  which  have 
been  found  in  southern  New  York,  and  near  New  Haven 
in  Connecticut. 

Among  the  Mammals  of  Europe  which  existed  before 
the  close  of  the  Champlain  period,  some  are  now  living  ; 
as  the  Reindeer,  Marmot,  Ibex,  Chamois,  Elk,  Wild  Boar, 
Goat,  Stag,  Aurochs,  Wolf,  Brown  Bear,  and  others. 


436  HISTORICAL  GEOLOGY. 


MAN. 

Prehistoric  Relics  of  Man  in  Europe.  —  The  earliest 
relics  of  Man  in  Europe  —  the  region  whose  prehistoric 
archaeology  has  been  most  thoroughly  explored  —  are  rude 
flint  implements,  as  arrowheads,  chisels,  etc. ;  flint  chip- 
pings,  or  the  chips  thrown  off  in  making  the  implements  ; 
rude  carvings ;  human  bones  and  skeletons  ;  the  bones 
of  the  animals  used  for  food,  split  lengthwise,  this  being 
done  to  get  at  the  marrow ;  charcoal,  and  other  remains 
of  fires.  They  occur  associated  with  the  remains  of  the 
Cave  Bear,  Cave  Hyena,  Cave  Lion,  Mammoth,  and  other 
species  which  have  either  become  extinct  or  migrated  to 
other  regions.  They  date  from  the  Champlain  period, 
and  perhaps,  in  part,  from  the  Glacial  period. 

1.  The  Paleolithic  Epoch.  —  As  the  only  implements 
of  early  Man  in  Europe  were  of  stone  or  bone,  the  era  in 
human  history  has  been  called  the  Stone  Age,  in  distinction 
from  the  Bronze  Age  and  the  Iron  Age,  in  which  Man  had 
acquired  the  use  of  metals.  These  three  stages  of  civili- 
zation (and,  for  Europe,  chronological  periods)  had  been 
long  recognized  by  students  of  European  archaeology. 
But  later  studies  made  it  manifest  that  the  Stone  Age  in 
Europe  not  only  included  a  vastly  greater  lapse  of  time 
than  the  two  later  ages  together,  but  included  widely 
different  types  of  culture.  It  became  necessary,  there- 
fore, to  subdivide  the  Stone  Age.  The  earliest  part  of 
that  age  has  been  designated  the  Paleolithic  epoch,  from 
the  Greek  TraXcwo?,  ancient,  and  \i6os,  stone.  Geologi- 
cally, it  may  be  correlated  with  the  Champlain  epoch,  and 
perhaps  with  the  latter  part  of  the  Glacial  epoch.  The 
Paleolithic  implements  are  never  polished,  and  are  of 
ruder  make  than  those  of  the  later  part  of  the  Stone  Age. 
Portions  of  skeletons  referred  to  this  era  have  been  found 
in  various  countries  of  Europe.  In  many  cases,  how- 
ever, the  evidence  of  age  is  more  or  less  dubious.  Some 


QUATERNARY  ERA.  437 

of  the  skulls  and  other  bones  present  features  which  are 
somewhat  simian  ;  but  this  is  not  true  of  all  the  supposed 
Paleolithic  remains.  The  skull  found  at  Engis  in  Belgium 
is  pronounced  by  Huxley  "a  fair  average  human  skull"  ; 
and  the  same  authority  declares  that  "  the  most  pithecoid 
of  human  crania  yet  discovered "  (the  skull  found  at 
Neanderthal  in  the  Rhine  valley)  can  in  no  sense  "be 
regarded  as  the  remains  of  a  being  intermediate  between 
Men  and  .Apes."  The  antiquity  of  neither  of  these 
famous  relics  is  free  from  doubt. 

2.  The  Reindeer  Epoch.  —  The  second  section  of  the 
European  Age  of  Stone  has  been  called  the  Reindeer, 
or  Mewlithic,  epoch.  By  many  archaeologists  it  is  con- 
sidered only  a  subdivision  of  the  Paleolithic  epoch.  It 
was  probably  the  time  of  transition  from  the  Cham- 
plain  to  the  Recent  epoch,  which  in  Europe  was  marked 
by  a  recurrence  of  Glacial  conditions  (page  427);  and 
the  deposits,  which  are  found  in  the  caves  of  southern 
France  and  elsewhere,  are  distinguished  by  the  occur- 
rence of  large  numbers  of  the  bones  of  the  Reindeer, 
along  with  the  human  relics.  The  flint  implements  of 
this  epoch  are  well  made,  but  are  still  exclusively  made 
by  chipping,  the  men  of  the  Reindeer  epoch  not  hav- 
ing developed  the  art  of  grinding  and  polishing  stone ; 
and  among  the  relics  there  are  implements  of  bone,  ivory, 
and  horn,  and  drawings  of  animals  upon  these  materials. 
One  of  these  drawings  from  southern  France,  made  on 
ivory,  is  copied  in  Fig.  462.  It  represents  the  hairy 
Elephant,  or  Mammoth  ;  and  shows  that  the  men  of  that 
epoch  were  familiar  with  the  Mammoth  as  a  living  animal. 
Remains  of  the  Elephant,  Cave  Bear,  Cave  Hyena,  Cave 
Lion,  occur  in  the  same  deposits,  and  also  others  of  exist- 
ing species,  as  the  Elk,  Ibex,  Aurochs,  etc.  Perfect  skel- 
etons of  Man  have  been  found  in  some  of  the  caverns. 
Those  of  southern  France  are  in  part  of  tall  stature, — 
5  feet  9  inches  to  6  feet,  —  having  well-shaped  heads,  and 
a  large  facial  angle  (85°).  One  supposed  to  belong  to 


438  HISTORICAL   GEOLOGY. 

this  epoch,  from  a  cave  at  Mentone  (on  the  Mediterranean, 
near  the  borders  of  France  and  Italy),  was  of  a  man  fully 
6  feet  in  height;  and  it  lay  buried  in  the  stalagmite  of  the 
cave,  with  flint  implements  and  shell  ornaments  around, 
and  a  chaplet  of  stag's  teeth  across  its  head. 

3.  The  Neolithic  Epoch.  —  A  third  epoch  is  named  the 
Neolithic  (from  z/e'o?,  new,  and  Xitfo?).  The  relics  include 
stone  implements  which  are  ground  and  polished,  as  well 
as  those  which  are  chipped  ;  also  broken  pottery,  and 
bones  of  the  Dog  and  (except  in  the  earliest  part  of  the 
epoch)  other  domestic  animals.  The  Neolithic  men  were, 
therefore,  in  a  much  more  advanced  stage  of  culture 

FIG.  462. 


Picture  of  Elephas  primigenius,  engraved  on  ivory,  x  |. 

than  those  of  the  preceding  epochs.  Remains  of  extinct 
Champlain  Mammals  (except  the  Irish  Deer)  and  of  ani- 
mals which  have  ceased  to  exist  in  central  and  southern 
Europe,  though  surviving  in  some  other  region  (as  the 
Reindeer),  are  absent.  Neolithic  man  belongs  unques- 
tionably to  the  Recent  period  of  geological  time.  The 
earth  and  its  fauna  and  flora  had  acquired  substantially 
their  present  condition. 

The  Neolithic  race  of  men  in  Denmark  resembled  the 
Laplanders.  Their  remains  are  found  in  shell  heaps  (the 
so-called  kjokkenmodingr,  or  kitchen  middens)  along  the 
shores  of  the  Baltic.  These  shell  heaps  are  relics  of  feasts, 


QUATERNARY  ERA.  439 

in  which  Oysters,  Mussels,  and  other  Mollusks  apparently 
formed  a  considerable  part  of  the  food. 

To  a  later  time  in  this  epoch  belong  the  earlier  lake 
dwellings  of  Switzerland  —  structures  built  on  piles  in  the 
lakes,  —  in  which  the  only  implements  are  of  stone  and 
other  non-metallic  materials.  But  in  the  later  lake  dwell- 
ings, about  the  western  Swiss  lakes,  there  are  bronze  imple- 
ments, and  these  are  of  the  Bronze  Age.  A  few  of  the  lake 
dwellings  belong  even  to  the  Iron  Age.  The  Neolithic  men 
of  the  lake  dwellings  were  no  longer  merely  hunters  and 
fishers,  but  agriculturists,  raising  wheat  .and  barley. 

Prehistoric  Relics  of  Man  in  Other  Countries.  —  In 
America,  the  Indians,  at  the  time  of  the  discovery  of  the 
continent  by  Europeans,  were  mainly  in  a  Neolithic  stage 
of  culture.  Rude  stone  implements  have  been  found  in 
various  localities,  which  have  been  considered  to  belong 
to  an  earlier  Paleolithic  race  ;  but  the  evidence  of  such 
an  early  race  is  less  satisfactory  than  in  Europe,  since  in 
some  cases  the  age  of  the  deposit  is  in  dispute,  and  the 
localities  have  not  in  general  been  verified  by  a  succession 
of  discoveries.  The  human  skull  reported  from  an  ancient 
gravel  in  Calaveras  County,  California,  is  probably  an 
authentic  relic,  and  is  associated  with  extinct  species  of 
Mammals.  It  is,  however,  similar  to  that  of  a  modern 
Indian,  and  the  implements  in  the  gravels  are  of  Neolithic 
type.  In  that  locality,  some  of  the  Pliocene  and  Pleisto- 
cene Mammalia  may  have  survived  to  a  later  date  than 
in  most  other  regions. 

In  1894,  Dr.  Dubois  announced  the  discovery,  in  Java, 
of  a  portion  of  a  skull,  two  teeth,  and  a  femur,  which  he 
considered  to  belong  to  a  manlike  Ape,  and  which  he 
named  Pithecanthropus  erectus.  The  remains  appear  to 
be  human,  but  the  skull  shows  simian  characters  even 
more  strongly  marked  than  those  of  the  Neanderthal 
skull  and  others  which  have  been  found  in  Europe.  It 
is  uncertain  whether  the  formation  in  which  the  relics 
were  found  is  Pleistocene  or  Pliocene. 


440 


HISTORICAL   GEOLOGY. 


The  evidence  seems  to  render  it  probable  that  the  ear- 
liest of  prehistoric  races,  ranging  from  the  East  Indies  to 
western  Europe,  possessed  features  more  simian  than  are 
characteristic  of  any  race  of  men  now  in  existence. 

Modern  Human  Relics.  —  In  modern  deposits,  buried 
coins,  statues,  temples,  cities,  are  found  among  the  earth's 
fossils,  contrasting  strangely  with  the  remains  of  the  species 

FIGS.  463,  464. 


Human  skeleton  from  Guadeloupe. 


Conglomerate  containing  coins. 


with  which  the  history  of  the  world's  life  began.  Fig. 
464  represents  a  coin  conglomerate,  containing  coins  of 
silver,  of  the  reign  of  Edward  I.,  found  at  a  depth  of  ten 
feet  below  the  bed  of  the  river  Dove  in  England;  and 
Fig.  463,  a  portion  of  a  human  skeleton  firmly  imbedded 
in  a  modern  shell  limestone  of  Guadeloupe,  the  former 
owner  of  which  was,  less  than  three  centuries  ago,  a 
fighting  Carib. 

Man  at  the  Head  of  the  System  of  Life.  —  With  the 
creation  of  Man  a  new  era  opens  in  geological  history.  In 
earliest  time  only  matter  existed  —  dead  matter.  Then 
appeared  life  —  unconscious  life  in  the  plant,  conscious 


QUATERNARY   ERA.  441 

and  intelligent  life  in  the  animal.  Ages  rolled  by,  with 
varied  exhibitions  of  animal  and  vegetable  life.  Finally 
Man  appeared,  a  being  made  of  matter  and  endowed  with 
life,  but,  more  than  this,  partaking  of  a  spiritual  nature. 
The  systems  of  life  belong  essentially  to  time ;  but  Man, 
through  his  spirit,  belongs  to  the  infinite  future.  Thus 
gifted,  man  is  the  only  being  capable  of  reaching  toward 
a  knowledge  of  himself,  of  nature,  or  of  God.  He  is, 
therefore,  the  only  being  capable  of  conscious  obedience 
or  disobedience  to  moral  law,  the  only  being  subject  to 
degradation  through  excesses  of  appetite  and  violation  of 
moral  law,  the  only  being  with  the  will  and  power  to 
make  nature's  forces  his  means  of  progress. 

Man  shows  his  exalted  nature  in  his  material  structure. 
His  fore  limbs  are  not  made  for  locomotion,  as  in  all  quad- 
rupeds ;  they  are  removed  from  the  locomotive  to  the 
cephalic  series,  being  fitted  to  serve  the  head,  and  espe- 
cially the  intellect  and  soul.  Man  stands  erect,  his  body 
placed  wholly  under  the  brain,  to  which  it  is  subservient. 
His  whole  outer  being,  in  these  and  other  ways,  shows 
forth  the  divine  nature  of  the  inner  being. 

EXTINCTION  OF  SPECIES  IN  MODERN  TIMES. 

Species  are  becoming  extinct  in  the  present  epoch, 
as  in  the  past.  Man  is  now  a  prominent  means  of  this 
destruction.  The  Dodo,  a  large  bird  looking  like  an 
overgrown  chicken  in  its  plumage  and  wings,  was  abun- 
dant in  the  island  of  Mauritius  until  late  in  the  seventeenth 
century.  In  New  Zealand  have  been  found  remains  of 
almost  twenty  species  of  Ostrich-like  Birds,  known  collec- 
tively under  the  native  name  Moa,  and  referred  to  the 
genera  .Dinornis,  Meionornis,  Palapteryx,  etc.  The  largest 
species  was  10  or  12  feet  in  height,  and  the  tibia  ("drum- 
stick ")  30  to  32  inches  long.  Some  species  at  least  of  the 
Moas  may  have  survived  until  within  a  century  or  two. 
In  Madagascar  remains  of  a  still  larger  bird,  but  of  similar 
character,  occur,  called  JEpyornis ;  its  egg  is  over  a  foot 


442  HISTORICAL  GEOLOGY. 

(13J-  inches)  long.  The  Great  Auk,  a  bird  of  northern 
seas,  has  become  extinct  within  the  present  century ;  the 
last  was  seen  in  1844.  These  are  a  few  examples  of  the 
modern  extinction  of  species. 

The  progress  of  civilization  tends  to  restrict  forests  and 
forest  life  to  narrower  and  narrower  limits.  The  Buffalo 
once  roamed  over  North  America  to  the  Atlantic,  but  is 
now  practically  extinct,  except  where  it  is  under  human 
protection.  The  Beaver,  Wolf,  Bear,  and  Wild  Boar 
were  .formerly  common  in  Great  Britain,  but  are  now 
wholly  exterminated. 

GENERAL   OBSERVATIONS   ON  CENOZOIC  TIME. 

Contrast  between  the  Tertiary  and  Quaternary  Eras  in 
Geographical  Progress.  —  The  study  of  Cenozoic  time  has 
brought  out  the  contrast  in  the  geological  work  of  the 
Tertiary  and  Quaternary  ages. 

The  Tertiary  in  North  America  carried  forward  the  work 
of  rock-making,  and  of  extending  the  limits  of  the  dry  land 
southward,  southeastward,  and  southwestward,  which  had 
been  in  progress  ever  since  Archsean  time. 

The  Quaternary  transferred  the  scene  of  operations  to 
the  broad  surface  of  the  continent,  and  especially  to  its 
middle  and  higher  latitudes. 

Through  the  Tertiary,  the  higher  mountains  of  the 
globe  had  been  rising,  and  the  continents  extending  ;  and 
hence  the  great  rivers  with  their  numerous  tributaries  — 
which  are  the  offspring  of  great  mountains  on  great  con- 
tinents—  channeled  out  the  mountains  and  made  valleys 
and  crested  heights.  In  the  Glacial  epoch  this  work  went 
forward  with  special  energy.  The  exposed  rocks  yielded 
before  the  moving  glacier,  and  the  fragments  torn  from 
the  ledges,  with  the  disintegrated  material  which  had 
accumulated  in  pre-Glacial  time,  were  carried  along  to  be 
distributed  over  the  continental  surface.  Torrents,  fed 
by  the  melting  ice,  were  also  at  work,  with  perhaps  even 


CENOZOIC   TIME.  443 

greater  abrading  power  than  the  ice.  Thus  the  excava- 
tion of  valleys  and  the  shaping  of  hills  and  mountains 
were  everywhere  in  progress.  In  the  Champlain  period, 
the  low  level  at  which  the  land  lay,  and  the  melting  of  the 
ice,  with  the  dropping  of  its  earth  and  stones,  enabled  the 
flooded  streams  to  fill  the  great  valleys  deep  with  allu- 
vium. In  the  Recent  period,  which  followed,  the  upward 
movements  of  the  land  led  to  a  terracing  of  the  Champlaiu 
deposits  along  the  seashores  and  about  the  lakes  and  rivers. 

Thus,  under  the  rending,  eroding,  and  transporting 
power  of  fresh  water,  frozen  and  unfrozen,  —  eminently 
the  great  Quaternary  agent,  —  in  connection,  probably, 
with  high-latitude  oscillations  of  the  earth's  crust,  the 
making  of  the  earth  was  finally  completed. 

Life. — In  Cenozoic  time,  as  in  the  preceding  seons,  species 
were  disappearing  and  others  took  their  places.  The  Mam- 
mals of  the  early  Eocene  are  different  in  species  from  those 
of  the  later;  and  these  from  the  Miocene,  the  Miocene  from 
the  Pliocene,  and  the  Pliocene  from  the  Quaternary. 

According  to  the  present  state  of  discovery,  Mammals 
commenced  in  Mesozoic  time,  late  in  the  Triassic  era, 
and  the  Mesozoic  species  were  probably  all  Monotremes 
and  Marsupials.  They  were  the  precursor  species,  pro- 
phetic of  that  expansion  of  the  new  type  which  was  to 
take  place  after  the  Age  of  Reptiles  had  closed.  In  the 
early  Eocene,  at  the  opening  of  the  Age  of  Mammals, 
appeared  Ungulates  and  Creodonts  of  large  size.  The 
earliest  Ungulates  (such  as  Phenacodm,  Fig.  443,  page 
395)  were  scarcely  distinguishable  from  the  earliest  repre- 
sentatives of  the  Carnivores  (Creodonts);  but  more  typical 
representatives  of  both  groups  appeared  before  the  close 
of  the  Eocene.  In  the  early  Tertiary  there  were  Perisso- 
dactyls  allied  to  the  Tapir  and  Rhinoceros,  and  Artiodac- 
tyls  allied  to  the  Hog.  Proboscideans  commenced  in  the 
Miocene,  though  the  Elephant  proper  appeared  first  in  the 
Pliocene.  Deer  and  Antelopes  commenced  in  the  Miocene, 
Oxen  in  the  Pliocene. 


444  HISTOKICAL   GEOLOGY. 


GENERAL    OBSERVATIONS    ON    GEOLOGIC 
GAL   HISTORY. 

LENGTH  OF  GEOLOGICAL  TIME. 

By  employing  as  data  the  relative  thickness  of  the  forma- 
tions of  the  geological  ages,  estimates  have  been  made  of 
the  time  ratios  of  those  ages,  or  their  relative  lengths 
(pages  317,  379).  These  estimated  time  ratios  for  the 
Paleozoic,  Mesozoic,  and  Cenozoic,  are  12  :  3  : 1.  But  the 
numbers  may  be  much  altered  when  the  facts  on  which 
they  are  based  are  more  correctly  ascertained.  It  is  quite 
certain  that  the  Eopaleozoic  (Cambrian  and  Lower 
Silurian)  was,  at  the  least,  three  times  as  long  as  either 
the  Devonian  or  Carboniferous,  and  longer  than  the 
entire  Neopaleozoic ;  and  probable  that  Mesozoic  time 
was  not  less  than  three  times  as  long  as  Cenozoic. 

Hence  comes  the  striking  conclusion  that  the  longest  age 
of  the  world  since  life  began  was  the  earliest — when  the 
earth's  population  (with  the  exception  of  a  few  Insects 
and  Fishes,  in  the  latter  part  of  the  time)  included  only 
marine  Invertebrates.  And  the  time  of  the  earth's  begin- 
nings before  the  introduction  of  life  must  have  exceeded 
in  length  all  subsequent  time. 

The  actual  lengths  of  these  ages  it  is  not  possible  to  de- 
termine even  approximately.  All  that  Geology  can  claim 
to  do  is  to  prove  the  general  proposition  that  Time  is 
long.  If  time  from  the  commencement  of  the  Cambrian 
included  48  millions  of  years,  which  most  geologists  would 
pronounce  too  low  an  estimate,  the  Paleozoic  part,  ac- 
cording to  the  above  ratio,  would  comprise  36  millions, 
the  Mesozoic  9  millions,  and  the  Cenozoic  3  millions. 

One  of  the  means  of  estimating  the  length  of  past  time 
is  that  afforded  by  the  rate  of  recession  of  the  Falls  of 
Niagara.  The  river  below  the  Falls  flows  northward  in 
a  deep  gorge,  with  high  rocky  walls,  for  seven  miles, 
toward  Lake  Ontario.  It  is  reasonably  assumed  that  the 


GEOGRAPHICAL   PROGRESS.  445 

gorge  has  been  cut  out  by  the  river,  for  the  river  is 
now  accomplishing  work  of  this  very  kind.  By  certain 
fossiliferous  Quaternary  beds  over  the  country  bordering 
the  present  walls,  and  by  other  evidence,  it  is  proved  that 
at  least  about  six  miles  of  the  present  gorge,  and  probably 
the  whole  seven  miles,  was  made  after  the  retreat  of  the 
ice  sheet  of  the  Glacial  period  from  that  part  of  the  coun- 
try. A  comparison  of  surveys  made  respectively  in  1842 
and  1886  shows  that  the  recession  of  the  apex  of  the  Horse- 
shoe Fall  during  that  time  has  been  at  the  rate  of  about 
four  feet  per  year.  On  the  basis  of  that  determination, 
the  time  occupied  in  the  erosion  of  the  entire  gorge  has 
been  estimated  at  from  6000  to  10,000  years.  It  is,  how- 
ever, believed  by  many  geologists  that,  during  a  part  of 
the  time,  the  water  of  the  Upper  Lakes  (Superior,  Michi- 
gan, Huron)  was  diverted  into  another  channel.  On  that 
supposition,  the  estimate  of  the  time  required  for  the  cut- 
ting must  be  considerably  increased  —  perhaps  to  about 
30,000  years.  In  any  case,  when  it  is  considered  that  the 
work  has  been  done  in  a  small  fraction  of  the  latest  and 
shortest  of  the  geological  eras,  the  calculation  may  be 
regarded  as  establishing,  at  least,  the  proposition  that 
Time  is  long,  although  it  affords  no  satisfactory  numbers. 

Besides  the  estimates  of  geological  time  based  on  proc- 
esses of  erosion  and  sedimentation,  other  estimates  have 
been  made  by  physicists  based  on  the  conditions  of  cooling 
of  the  earth  and  the  sun. 

While  neither  the  geological  nor  the  physical  modes  of 
calculation  can  yield  any  certain  results  in  the  present 
state  of  our  knowledge,  it  may  be  considered  probable 
that  geological  time  from  the  beginning  of  the  Cambrian 
is  measured  by  tens  of  millions,  rather  than  by  millions, 
or  by  hundreds  of  millions,  of  years. 

GEOGRAPHICAL  PROGRESS  IN  NORTH  AMERICA. 

The  principal  steps  of  progress  in  the  continent  of  North 
America  are  here  recapitulated:  — 


446  HISTORICAL   GEOLOGY. 

1.  The  continent  at  the  close  of  the  Archsean  lay  spread 
out  mostly  beneath  the  ocean  (map,  page  237).     Although 
thus  submerged,  its  outline  was  nearly  the  same  as  now. 
The  dry  land  lay  mostly  to  the  north,  as  shown  on  the 
map.     The  form  of  the  main  mass  approximated  to  that 
of  the  letter  V,  and  the  arms  of  the  V  were  nearly  parallel 
to  the  present  coast  lines. 

2.  Through  the  Paleozoic  ages,  as  the  successive  periods 
passed,  the  dry  land  gradually  extended  itself  southward, 
owing  to  a  gradual  emergence;  that  is,  the  sea  border  at 
the  close  of  the  Lower  Silurian  was  probably  as  far  south 
as  the  Mohawk  valley  in  New  York ;  at  the  close  of  the 
Upper  Silurian  it  extended  along  not  far  from  the  north 
end  of  Cayuga  Lake  and  Lake  Erie;  and  by  the  close  of 
the  Devonian  era  the  state  was  a  portion  of  the  dry  land 
nearly  to  its  southern  boundary.     This  southward  prog- 
ress of  the  sea  border  in  New  York  may  be  taken  as  an 
example    of   what   occurred   along   the    borders    of    the 
Archasan    farther    west.      In    other    words,    there    was 
through  the    Cambrian,   Silurian,    and  Devonian  ages  a 
gradual  extension  of  the  dry  part  of  the  continent  south- 
eastward and  southwestward. 

By  the  close  of  the  Carboniferous  era,  or  before  the  open- 
ing of  Mesozoic  time,  the  dry  portion  appears  to  have  so 
far  extended  southwardly  as  to  include  nearly  all  the  area 
east  of  the  Mississippi,  at  least  north  of  the  Gulf  States, 
along  with  a  part  of  that  west  of  the  Mississippi,  as  far  as 
the  middle  of  Kansas. 

3.  During  the  Paleozoic  ages,  rock  formations  were  in 
progress  over  large  parts  of  the  submerged  portions  of  the 
continent ;    and  some  vast  accumulations  of   sand  were 
made  as  drifts  or  dunes  over  the  flat  shores  and  reefs. 
These  rock  formations  had  in  general  ten  times  the  thick- 
ness along  the  Appalachian  region  which  they  had  over  the 
interior  of  the  continent ;  and  they  were  mostly  f  ragmental 
deposits  in  the  former  region,  while  mostly  limestones  in 
the  latter.     Hence  two  important  conclusions  follow  :  — 


GEOGRAPHICAL  PROGRESS.  447 

First.  The  Appalachian  region  was  through  much  of 
the  time  a  sea-border  region,  receiving  the  debris  from 
the  land.  There  was  a  strip  of  emerged  land  along  the 
Appalachian  region  at  the  close  of  Archaean  time,  and 
Cambrian  and  Lower  Silurian  deposits  were  formed  on 
both  sides  of  the  emerged  land.  At  the  close  of  the  Lower 
Silurian,  a  considerable  region  emerged,  adjoining  the 
Archaean  area  on  the  east.  Along  the  western  shore  of 
this  broad  area  of  dry  land,  the  debris  accumulated  to 
form  the  later  Paleozoic  deposits.  At  the  same  time  the 
Interior  region  was  a  mediterranean  sea,  whose  pure  waters 
over  large  areas,  mostly  free  from  mechanical  sediments, 
afforded  the  conditions  for  a  luxuriant  growth  of  the 
marine  life  whose  skeletons  are  the  material  for  the  mak- 
ing of  limestone. 

Secondly.  The  Appalachian  region  was  undergoing 
great  changes  of  level,  the  deposits  having  been  made  in 
shallow  waters  ;  the  region  was  slowly  sinking,  not  faster 
than  the  rate  of  deposition,  and  the  amount  of  subsidence 
exceeded  by  ten  times  that  in  the  Interior  Continental 
region. 

4.  In  this  Appalachian  region,  the  Taconic  range  (and 
probably   a   system    of   contemporaneous   ranges   farther 
south)  was  upturned,  rendered  metamorphic,  and  elevated 
above  the  ocean's  level,  at  the  close  of  the  Lower  Silurian  ; 
and  at  the  same  time  the  valley  of  Lake  Champlain  and 
Hudson  River  was  formed,  if  not  earlier  begun.     At  the 
same  time,  also,  the  Atlantic  Border  region  south  of  New 
York  emerged  by  an  extensive   geanticlinal  movement, 
forming  a  land  mass  of  unknown  breadth,  whose  denuda- 
tion in  later  Paleozoic  time  furnished  material  for  the 
thick  sediments  of  the  Appalachian  range  proper. 

5.  As  Paleozoic  time  closed,  an  epoch  of  revolution 
occurred,  in  which  the  rocks  of  the  Appalachian  region 
south  of  New  York  arid  west  of  the  Piedmont  region  of 
ancient  crystalline  rocks  underwent  (1)   extensive  flex- 
ures or  foldings;   (2)  immense  faultings  in  some  parts; 


448  HISTORICAL   GEOLOGY. 

(3)  consolidation,  and,  in  some  eastern  portions,  some 
degree  of  metamorphism,  with  the  conversion  of  bitumi- 
nous coal  into  anthracite.  These  changes  affected  the 
region  from  New  York  to  Alabama.  The  effects  of  heat 
and  uplift  were  more  decided  toward  the  Atlantic  than 
toward  the  Interior,  showing  that  the  force  producing  the 
great  results  was  exerted  in  a  direction  from  the  Atlantic, 
or  from  the  southeast  toward  the  northwest.  The  Appa- 
lachian Mountains  proper  were  then  made ;  and  they 
were,  consequently,  in  existence  when  the  Mesozoic  era 
opened. 

These  mountains  are  parallel  to  the  eastern  outline  of 
the  original  Archaean  continent. 

Some  disturbances  probably  took  place  at  the  same  time 
in  the  Great  Basin  ;  but  no  general  revolution  on  the 
Pacific  side  comparable  to  that  on  the  Atlantic. 

In  Europe,  also,  this  epoch  of  revolution  was  a  time  of 
mountain-making. 

6.  In  early  Mesozoic  time  (the  continent  being  largely 
dry  land,  as  stated  in  the  latter  part  of  §  2),  long  depres- 
sions in  the  surface  of  the  continent,  made  in  the  course 
of  the  Appalachian  revolution,  and  situated  between  the 
Appalachians   and   the  sea  border,   were    brackish-water 
estuaries,  or  were  occupied   by  fresh-water  marshes  and 
streams ;    and  Mesozoic  sandstones,  shales,  and  coal  beds 
were  formed  in  them.     The  Connecticut  Valley  region  of 
Mesozoic  rocks  (page  332)  is  one  example.     At  the  same 
time  there  were  formations  in  progress  over  the  Rocky 
Mountain  region,  a  vast  area  from  which  the  sea  was  not 
excluded,  or  only  in  part.     At  the  close  of  the  Jurassic 
period,  the  Sierra  Nevada  and   some  other  great  ranges 
on  the  western  side  of  the  continent  were  made. 

7.  In  the  later  Mesozoic,  or  the   Cretaceous  era,  the 
Atlantic  and  Gulf  Borders  of  the  continent  were  under 
water  (the  Atlantic  geanticline  formed  at  the  close  of  the 
Lower  Silurian  having  become  submerged),  and  received 
a  deposit   of   Cretaceous   rocks.     The   Western  Interior 


GEOGRAPHICAL  PROGRESS.  449 

sea,  opening  south  into  the  Gulf  of  Mexico,  still  existed, 
and  was  probably  for  the  most  part  a  deeper  and  clearer 
sea  than  in  the  earlier  Mesozoic.  Deposits  were  made  in 
it  over  a  very  large  part  of  the  great  region  reaching 
from  Iowa  on  the  east  to  the  Colorado  on  the  west,  and 
northward  probably  to  the  Arctic  Ocean.  The  Pacific 
Border  was  also  receiving  an  extension  like  the  Atlantic. 

8.  Mesozoic,  like  Paleozoic,  time  closed  with  a  revolu- 
tionary epoch  of  mountain-making;    but  the  theater  of 
this  Laramide,  or  post-Mesozoic,   revolution  was  on  the 
western  side  of  the  continent.     The  elevation  extended 
along  the  whole  line  of  the  summit  region  of  the  Rocky 
Mountains  from  near  the  Arctic  Ocean  to  central  Mexico  ; 
and  in  all  probability  the  long  line  of  the  Andes  shared 
in   the   movement.       The    Rocky    Mountain   and    Sierra 
ranges  are  parallel  to  the  western  arm  of  the  Archaean  V, 
as  the  Taconic  and  Appalachian  ranges  are  parallel  to  its 
eastern  arm. 

9.  In  the  Dearly  Cenozoic,  or  the  Tertiary  era,  the  ex- 
tension of  the  Atlantic  and  Pacific  Borders  was  still  con- 
tinued.    With  its  close  the  progress  of  the  continent  in 
rock-making  southeastward  and  southwestward  was  very 
nearly  completed. 

The  Interior  sea,  after  the  Laramide  revolution,  became 
dry  land,  except  remnants  left  as  great  fresh-water  lakes, 
a  transition  from  marine  to  terrestrial  conditions  being 
shown  by  the  coal-bearing  strata  of  the  Laramie  epoch. 
During  the  Eocene  Tertiary,  the  Ohio  and  Mississippi 
emptied  into  a  bay  of  the  Gulf  of  Mexico,  just  where  they 
now  join  their  waters;  at  the  close  of  the  Eocene  the  Ohio 
had  taken  a  secondary  place  as  a  tributary  of  the  Missis- 
sippi. The  great  Missouri  River,  now  the  main  trunk  of 
the  Interior  river  system,  began  its  existence  after  the 
Cretaceous  period,  and  reached  its  full  size  only  toward 
the  close  of  the  Tertiary,  when  the  Rocky  Mountains 
finally  attained  their  full  height. 

10.  The  continent  being  thus  far  completed,  as  the  Qua- 


450  HISTORICAL  GEOLOGY. 


. 


ternary  Age  was  drawing  on,  operations  changed  from 
those  causing  southern  extension,  to  those  producing 
movements  of  ice  and  fresh  waters  over  the  land,  especially 
in  the  higher  latitudes;  and  thereby  the  surface  of  the 
continent  acquired  its  present  character. 

PROGRESS  OF  LIFE. 

In  the  summary  of  the  characteristics  of  the  successive 
aeons  and  eras  of  geological  time  given  on  page  233,  the 
student's  attention  was  called  to  two  generalizations  :  first, 
that  in  the  progress  of  time  there  has  been  an  increasing 
approximation  to  the  flora  and  fauna  of  the  present  age  ; 
second,  that  there  has  been  a  rise  in  the  grade  of  plants 
and  animals  represented.  It  was  then  remarked  that  these 
generalizations  were  strikingly  in  accord  with  the  theory 
of  evolution,  now  almost  universally  adopted.  The  student 
is  now  prepared  to  take  a  fuller  survey  of  the  general  laws 
of  progress  in  the  history  of  life,  and  to  recognize  the 
significance  of  those  laws  in  relation  to  evolution. 

It  would  be  inappropriate  in  this  place  to  discuss  the 
evidences  of  evolution  outside  of  the  sphere  of  geology  and 
paleontology  —  those,  for  instance,  which  are  afforded  by 
the  homologies  of  structure  maintained  in  spite  of  wide 
diversity  of  function,  by  rudimentary  organs,  by  the  laws 
of  embryology,  by  the  facts  of  geographical  distribution, 
and  by  the  difficulties  and  uncertainties  of  zoological  and 
botanical  classification.  Only  the  bearings  of  the  geologi- 
cal history  of  plants  and  animals  can  be  here  presented. 

The  concurrence  of  evidence  from  many  different  sources 
has  brought  about  a  substantially  unanimous  opinion 
among  naturalists,  that  the  existing  species  of  plants  and 
animals  have  originated  by  descent  with  modification,  from 
species  that  preceded  them  in  geological  time,  and  these, 
in  turn,  from  still  earlier  species,  and  so  on  to  the  simplest 
living  forms  with  which  life  is  supposed  to  have  com- 
menced. There  is,  however,  much  uncertainty  and  much 
difference  of  opinion  in  regard  to  the  method  of  evolution 


PROGRESS   OF   LIFE.  451 

and  the  forces  which  have  operated  in  the  production  of 
the  result.  It  is  generally  believed  that  the  changes  from 
generation  to  generation,  which  have  resulted  in  the  evo- 
lution of  new  species,  are  mainly  due,  directly  or  indirectly, 
to  the  influence  of  environment.  Some  naturalists  attrib- 
ute very  much  to  the  direct  influence  of  environment, 
assuming  that  the  effects  of  use  or  disuse  of  organs,  and 
other  effects  produced  in  the  lifetime  of  individuals  by  the 
environment,  will  be  inherited  in  greater  or  less  degree 
by  their  offspring,  and  may,  therefore,  be  accumulated 
from  generation  to  generation.  Others  believe  that  com- 
paratively little  is  due  to  the  direct  influence  of  environ- 
ment. All  agree  that  a  most  potent  influence  in  evolution 
is  the  indirect  influence  of  environment,  as  formulated 
in  Darwin's  principle  of  natural  selection.  According  to 
this  principle,  those  individuals  in  each  generation  whose 
peculiarities  of  organization  are  most  thoroughly  adapted 
to  the  environment  will  have  the  greatest  chance  of  sur- 
viving to  maturity  and  leaving  offspring.  In  this  manner, 
whatever  may  be  the  causes  of  variation,  all  variations 
which  place  the  individual  more  in  harmony  with  its  en- 
vironment will  tend  to  be  preserved  and  accumulated  from 
generation  to  generation.  Some  naturalists  have  imagined 
innate  tendencies  to  progress  in  the  organization  of  species, 
and  other  occult  or  transcendental  forces  tending  to  evo- 
lution. There  may  be  causes  of  evolutionary  change 
as  yet  entirely  unknown.  In  so  far  as  evolution  depends, 
either  directly  or  indirectly,  upon  the  influence  of  environ- 
ment, it  is  obvious  that  evolutionary  changes  in  flora  and 
fauna  must  have  gone  on  rapidly  only  when  rapid  changes 
have  taken  place  in  the  environment.  The  geological 
record  seems  to  indicate  that,  in  every  region  of  the  globe, 
there  have  been  long  periods  of  comparative  stability  in 
geographical  conditions,  alternating  with  epochs  of  com- 
paratively rapid  change.  Evolution  cannot,  therefore, 
have  progressed  at  uniform  rate  through  geological  time, 
but  periods  of  comparatively  rapid  evolution  must  have 


452  HISTORICAL   GEOLOGY. 

alternated  with  long  ages  of  approximately  stationary  con- 
ditions. It  is  uncertain  to  what  extent  the  evolution  of 
new  species  has  taken  place  by  the  accumulation  of  minute 
variations  from  generation  to  generation,  and  to  what 
extent  occasional  abrupt  variations  have  contributed  to 
that  result.  On  the  latter  supposition,  it  is  obvious  that 
the  series  of  intermediate  forms,  which  must  have  existed 
between  an  ancestral  species  and  a  species  derived  from  it, 
would  have  shown  much  less  fine,  gradations  than  on  the 
former. 

The  General  Fact  of  Progress  in  Life.  —  In  the  survey 
of  geological  history  which  the  student  has  now  completed, 
he  will  have  been  impressed  continually  with  the  general 
fact  of  progress.  In  the  Cambrian,  the  only  plants  were 
Seaweeds.  Acrogens  made  their  first  appearance  in  the 
Lower  Silurian,  and  became  abundant  in  the  Devonian 
and  Carboniferous.  Gymnosperms  first  appeared  in  the 
Devonian,  and  culminated  in  the  Mesozoic.  Angiosperms 
began  in  the  Cretaceous,  and  attain  their  greatest  develop- 
ment at  the  present  time.  The  Echinoderms  of  the  Cam- 
brian were  Crinoids,  the  lowest  class  of  the  subkingdom. 
The  Echinoids,  the  highest  of  the  classes  possessed  of 
well-developed  skeletons,  in  that  subkingdom,  appeared 
as  early  as  the  Lower  Silurian  ;  but  the  highest  group  of 
this  class,  the  Irregular  Echinoids,  did  not  appear  till  the 
Jurassic.  The  class  of  Gastropods  commenced,  indeed,  in 
the  Cambrian,  but  the  higher  families  of  that  class,  char- 
acterized by  the  most  specialized  types  of  dentition,  did 
not  appear  until  the  Mesozoic.  Of  the  Cephalopods,  the 
lower  order,  the  Tetrabranchs,  appeared  in  the  Cambrian^ 
but  the  higher  order,  the  Dibranchs,  not  till  the  Triassic. 
The  most  of  the  Crustaceans  of  early  time  belonged  to 
the  lower  subclass,  the  Entomostracans.  The  higher  sub- 
class of  Malacostracans  was,  indeed,  represented  in  the 
Cambrian,  but  onl}7  by  its  lowest  order,  the  Leptostracans, 
an  order  somewhat  intermediate  in  character  between 
the  two  subclasses.  The  higher  orders  of  Crustaceans 


PROGRESS  OF  LIFE.  453 

appeared  much  later.  The  Macrurans  made  their  first 
appearance  in  the  Devonian,  and  Brachyurans  not  till  the 
Jurassic.  With  the  exception  of  some  Neuropters  and 
possibly  a  few  Beetles,  the  Hexapod  Insects  in  the  Pale- 
ozoic all  belonged  to  the  orders  with  incomplete  meta- 
morphosis. The  higher  orders  of  Insects,  exhibiting  dis- 
tinctly in  their  development  the  three  stages  of  larva,  pupa, 
and  imago  (complete  metamorphosis),  belong  to  Mesozoic 
and  Cenozoic  time.  The  highest  of  the  subkingcloms, 
the  Vertebrates,  did  not  appear  at  all  in  the  Cambrian. 
Fishes  first  appeared  in  the  Lower  Silurian,  Amphibians 
in  the  Devonian,  Reptiles  in  the  Permian,  Birds  and 
Mammals  not  till  the  Mesozoic.  The  Reptiles  of  the 
Permian  belonged  mostly  to  the  comparatively  low  order 
of  Rhynchocephala.  The  more  highly  organized  Dino- 
saurs and  Pterosaurs  did  not  come  in  till  Mesozoic  time. 
The  Birds  of  the  Jurassic,  arid  some  of  those  of  the  Cre- 
taceous, still  retained  characteristics  allying  them  to 
Reptiles.  The  Mammals  of  the  Triassic  were  probably 
all  Monotremes,  and  those  of  the  Jurassic  and  the  Creta- 
ceous probably  all  Monotremes  and  Marsupials.  The 
higher  subclass  of  Placentals  probably  made  its  first 
appearance  in  the  Eocene,  and  Man  himself  marks  the 
culmination  of  living  nature  in  the  Quaternary. 

Cephalization.  —  The  progress  of  animal  life  in  gen- 
eral, and  the  progress  within  each  group  of  the  animal 
kingdom,  involves  a  manifestation  in  increasing  intensity 
of  the  fore-and-aft  structure,  which  has  been  stated  (page 
58)  to  be  characteristic  of  animal  life.  Bilateral  symme- 
try takes  the  place  of  radial  symmetry,  as  shown  by  the 
contrast  between  the  Regular  Echinoids,  which  appeared 
even  in  the  Paleozoic,  and  the  Irregular  Echinoids,  which 
were  unknown  till  the  Jurassic.  The  posterior  portion 
of  the  body  tends  to  become  abbreviated,  and  power  and 
function  to  be  concentrated  in  the  organs  and  appendages 
of  the  anterior  portion  of  the  body,  as  is  seen  in  compar- 
ing the  Macrurans,  which  appeared  in  the  Devonian, 


454  HISTORICAL  GEOLOGY. 

with  the  Brachyurans,  which  first  appeared  in  the  Juras- 
sic. The  cephalic  nerve  mass,  or  brain,  acquires  increas- 
ing size  with  the  increasing  activity  and  intelligence  of 
the  animal.  See,  for  illustration,  the  figures  of  casts  of 
Mammals'  brains  on  page  397. 

Parallelism  of  Paleontology  and  Embryology.  —  Ag- 
assiz  long  ago  called  attention  to  the  fact  that,  in  their 
development,  many  animals  pass  through  embryonic  or 
larval  forms  more  or  less  closely  resembling  animals  of 
lower  grade,  which  appeared  in  earlier  geological  periods. 
The  Crabs,  through  all  of  their  earlier  stages  of  develop- 
ment, have  a  long  tail-like  abdomen,  such  as  is  permanent 
in  the  Shrimps  and  other  Macrurans.  The  embryo  Spider 
has  the  abdomen  segmented,  as  in  the  adult  of  the  more 
ancient  group  of  Scorpions.  Indeed,  some  of  the  earliest 
Spiders,  in  the  Carboniferous  period,  show  traces  of  this 
segmentation  in  the  adult.  The  modern  Ganoids  and 
Teleosts  pass  through  an  embryonic  stage,  in  which  they 
have  heterocercal  tails  like  the  Ganoids  of  the  Paleozoic. 
The  embryos  of  Reptiles,  Birds,  and  Mammals  have  on  each 
side  of  the  neck  a  row  of  gill  slits  like  those  of  Sharks. 

Progress  from  Generalized  to  Specialized  Forms.  —  It 
was  remarked  on  page  396  that  the  representatives  respec- 
tively of  the  Ungulates  and  the  Carnivores  in  the  earli- 
est Eocene  are  scarcely  distinguishable  from  each  other ; 
whereas,  in  the  progress  of  time,  the  divergent  evolution 
has  led  to  a  stronger  accentuation  of  the  characters  of  the 
respective  groups,  as  is  seen  when  we  contrast  the  limbs 
or  the  dentition  of  the  Horse  and  the  Cat.  This  case  of 
the  Tertiary  Mammals  well  illustrates  a  general  law.  As 
we  go  back  in  geological  time,  the  lines  of  descent  appear 
to  converge,  indicating  that  forms  now  widely  separated 
may  have  been  derived  by  divergent  modification  from 
a  common  ancestry.  The  Ganoids,  whose  scales  are  pre- 
served in  Lower  Silurian  rocks,  appear  thus  to  have  formed 
the  starting  point  of  two  divergent  lines  of  evolution.  In 
one  direction  the  accentuation  of  piscine  characters  resulted 


PROGRESS   OF  LIFE.  455 

in  the  Homocercal  Ganoids  and  Teleosts,  while  the  other 
line  ascended  through  the  Dipnoans  to  the  Amphibians 
and  thence  to  the  higher  classes  of  Vertebrates.  It  was 
long  ago  pointed  out  by  Agassiz  that  the  earliest  repre- 
sentatives of  a  group  of  animals  often  possessed  character- 
istics which  appeared  to  connect  them  with  some  other 
group.  Such  forms  were  called  by  him  synthetic  types. 
By  others  they  have  been  named  comprehensive  types. 
Numerous  examples  of  such  comprehensive  types  occur 
in  geological  history,  and  it  is  noteworthy  that  they  have, 
in  general,  become  extinct  or  nearly  so.  The  Dipnoans, 
blending  with  the  characters  of  the  Fishes  the  pulmonary 
respiration  and  mode  of  articulation  of  the  lower  jaw 
characteristic  of  the  higher  Vertebrates ;  the  Labyrinth- 
odonts,  retaining  fishlike  structures  in  their  skeletons;  the 
Dinosaurs,  with  their  birdlike  limbs  and  pelvic  girdles ; 
the  Reptilian  Birds,  with  their  teeth,  and  long  tails,  and 
free  metacarpals ;  the  Monotremes,  with  their  reptilian 
characters  in  skeleton  and  reproductive  organs ;  —  are 
striking  examples  of  such  comprehensive  types. 

Progress  in  Diversification  of  Type.  —  It  is  a  note- 
worthy fact  that  no  classes  (in  the  classification  of  animals 
adopted  in  this  work),  and  very  few  orders,  have  ever 
become  extinct,  while  in  the  progress  of  geological  time 
several  classes  and  a  much  larger  number  of  orders  un- 
known in  the  Cambrian  have  been  introduced.  The 
result  has  been  an  increasing  diversification.  The  intro- 
duction of  higher  classes  and  orders  has  not  involved  the 
extinction  of  lower  types.  In  some  cases  evolution  has 
involved  a  degradation,  so  that  relatively  low  forms  have 
appeared  later  than  allied  forms  of  higher  grade.  The 
Ichthyosaurs,  Reptiles  degraded  to  fishlike  form  and  habit, 
did  not  appear  till  the  Triassic,  although  Reptiles  of  more 
normal  structure  were  already  in  existence  in  the  Permian. 
And,  while  the  true  Lizards  appeared  in  the  Jurassic,  the 
Snakes,  which  are  essentially  Lizards  that  have  suffered 
degradation  in  the  loss  of  limbs,  did  not  appear  until 


456  HISTORICAL  GEOLOGY. 

late  in  the  Cretaceous.  So,  among  Mammals,  although  a 
number  of  the  comparatively  normal  orders  of  Placentals 
were  represented  in  the  earliest  Eocene,  the  Whales  did 
not  appear  till  later  in  the  Eocene ;  and  the  Edentates, 
whose  degraded  character  is  shown  in  the  imperfection  of 
their  teeth,  did  not  appear  till  the  Miocene. 

Progress  from  Marine  to  Terrestrial  Life.  —  So  far 
-as  our  present  knowledge  goes,  the  life  of  the  Cambrian, 
both  vegetable  and  animal,  was  exclusively  marine.  The 
earliest  forms  of  life  were  probably  creatures  floating  on  the 
surface  of  the  sea ;  and  animals  developed  heavy  skeletons, 
and  took  to  crawling  upon  the  bottom  or  attaching  them- 
selves thereto,  only  in  a  later  stage  of  evolution  (see  page 
251).  In  the  Lower  Silurian  we  get  the  earliest  traces 
of  terrestrial  life,  in  Acrogens  and  Insects ;  but  it  is  not 
until  ths  Carboniferous  that  terrestrial  life  attains  a  very 
great  development ;  and  Phanerogams  among  plants,  and 
Insects,  Birds,  and  Mammals  among  animals,  the  forms 
of  terrestrial  life  now  dominant,  belong  chiefly  or  exclu- 
sively to  Mesozoic  and  Cenozoic  time. 

Increasing  Approximation  to  the  Present  Flora  and 
Fauna.  —  The  dominant  groups  of  Paleozoic  life  are,  with- 
out exception,  groups  which  are  now  comparatively  rare 
or  entirely  extinct.  The  gigantic  Sigillarids,  Lepidoden- 
drids,  and  Calamites  that  characterized  the  Carboniferous 
forests,  are  now  represented  by  insignificant  forms  which 
make  no  conspicuous  feature  in  the  vegetation.  Cya- 
thophylloid  Corals  have  only  doubtful  representatives 
after  the  Paleozoic.  Crinoids  decrease  in  abundance 
after  the  Paleozoic,  and  the  class  is  now  but  very  scan- 
tily represented.  The  groups  of  Cystoids  and  Blastoids 
are  exclusively  Paleozoic.  The  class  of  Brachiopods, 
whose  remains  in  the  early  Paleozoic  outweigh  all  other 
fossils  put  together,  is  now  reduced  to  an  insignificant 
remnant.  Of  Tetrabranch  Cephalopods,  the  genus  Nau- 
tilus is  now  the  sole  survivor.  The  Trilobites  and  the 
Placoderms  are  unknown  since  the  Paleozoic. 


PROGRESS  OF  LIFE.  45  T 

The  life  of  the  Mesozoic  shows  a  greater  resemblance  to 
ths  life  of  modern  times.  The  forests  of  Acrogens  are  suc- 
ceeded in  the  early  Mesozoic  by  forests  of  Gymnosperms, 
and  in  the  Cretaceous  Angiosperms  appear.  Brachio- 
pods  gradually  decline,  and  Lamellibranchs  gradually 
increase.  The  order  of  Tetrabranchs  is  represented  by  a 
vast  multitude  of  Ammonites,  but  associated  with  them 
are  Belemnites  and  other  representatives  of  the  Dibranchs. 
Insects  appear  in  increasing  numbers,  and  most  of  the 
higher  orders  are  represented.  Reptiles  attain  their  cul- 
mination ;  and,  before  the  close  of  the  Mesozoic,  the 
modern  groups  of  Teleost  Fishes,  Birds,  and  Mammals 
appear. 

The  Cambrian  fauna  includes  not  a  single  species  now 
surviving,  and  only  two  genera  represented  by  living  spe- 
cies, Lingula  and  Discina.  It  is  doubtful  even  whether 
ths  Cambrian  Brachiopods  referred  to  those  two  genera 
really  belong  to  them.  Before  the  close  of  the  Paleozoic, 
a  considerable  number  of  genera  appear  which  are  still 
represented  by  living  species ;  but  no  Paleozoic  species, 
either  of  plant  or  animal,  has  survived  to  the  present 
time,  with  the  doubtful  exception  of  a  few  species  of 
Carboniferous  Diatoms.  It  is  doubtful  whether  any  Meso- 
zoic species  of  animal,  except  a  few  species  of  Foraminifers, 
has  survived  to  the  present  day,  although  the  number  of 
genera  represented  by  living  species  becomes  considerable. 
With  the  beginning  of  the  Tertiary,  existing  species  of 
Invertebrates  make  their  appearance ;  and,  by  the  close  of 
the  Tertiary,  the  Plants  and  Invertebrates  are  mainly 
of  species  which  still  survive.  During  the  Quaternary, 
existing  species  of  Vertebrates  are  gradually  introduced. 

Gradual  Change  in  Genera  and  Species.  —  As  we  pass 
from  one  stratum  to  another  within  the  limits  of  a  forma- 
tion, it  may  generally  be  observed  that  some  species  dis- 
appear, and  others  take  their  place.  At  the  close  of  an 
epoch  or  a  period,  a  greater  proportion  of  the  life  is 
changed.  The  diagram  on  page  322,  showing  the  range 


458  HISTORICAL   GEOLOGY. 

of  some  of  the  principal  genera  of  Trilobites,  illustrates 
well  the  history  of  most  groups  of  organisms.  Each  class 
or  order  generally  appears  first  in  comparatively  small  num- 
bers of  species,  and  increases  to  a  culmination,  after  which 
it  may  gradually  decline ;  and  during  the  lifetime  of  a 
class  or  order  there  is  a  constant  appearance  and  disap- 
pearance of  genera  and  species.  It  is  not  certain  that  any 
species  represented  in  the  Paleozoic  appears  in  the  Meso- 
zoic,  and  scarcely  any  Mesozoic  species  appear  in  the  Cen- 
ozoic  ;  but,  at  the  present  day,  all  geologists  would  explain 
this  condition,  not  by  the  supposition  of  universal  exter- 
minations, but  by  reference  to  the  imperfection  of  the 
geological  record  (page  461). 

The  cause  of  the  extinction  of  species  must  be  supposed 
to  be,  in  general,  an  unfavorable  environment.  When 
the  environment  changes  so  that  a  species  is  no  longer  in 
harmony  with  it,  the  species  may  undergo  modification, 
if  the  change  of  environment  is  not  too  rapid,  or  may 
migrate,  if  areas  are  open  to  it  in  which  the  environment 
is  more  favorable.  Otherwise  it  must  become  extinct. 
Changes  of  climate  have  probably  been,  on  a  large  scale, 
the  most  important  influence  in  determining  such  evolu- 
tionary changes.  The  amount  of  heat  received  from  the 
sun  has  appreciably  declined  through  geological  time. 
The  water  vapor,  with  which  the  atmosphere  of  earlier 
ages  was  loaded,  has  been  gradually  condensed ;  and  the 
carbon  dioxide  has  been  gradually  removed  from  the 
atmosphere,  and  its  carbon  stored  in  various  forms  in 
the  crust  of  the  globe.  The  earth's  atmosphere  has 
thereby  become  less  absorptive  of  heat,  and  opposes  less 
resistance  to  the  radiation  of  heat  from  the  earth.  Oscil- 
lations of  level  of  the  earth's  crust  have  directly  affected 
the  temperature  of  the  areas  of  elevation  or  subsidence, 
and  have  indirectly  affected  the  temperature  of  other 
regions  by  changing  the  courses  of  ocean  currents.  While 
changes  of  climate  have  often  operated  simultaneously 
over  a  large  part  or  the  whole  of  the  surface  of  the  globe, 


PKOGEESS   OF  LIFE.  459 

every  movement  of  elevation  or  subsidence,  however  slight, 
has  made  local  changes  in  the  conditions  of  life.  Land 
has  been  converted  into  sea,  and  sea  into  land ;  salt  water 
has  given  place  to  fresh,  and  vice  versa;  muddy  shoals, 
receiving  detritus  from  the  shore,  have  given  place  to 
clear  seas  in  whose  pure  waters  corals  could  grow  luxu- 
riantly; and,  again,  the  debris  of  the  coral  gardens  has 
been  covered  with  mud  or  gravel.  Exterminations  of 
more  local  character  have  been  produced  by  various  catas- 
trophes, as  earthquake  waves  deluging  the  areas  of  land, 
volcanic  eruptions  heating  the  waters,  or  emanations  of 
gas  rendering  the  waters  poisonous.  And  the  conditions 
of  life  of  every  species  have  been  affected  not  only  by  the 
direct  influence  of  geographical  or  climatic  changes,  but 
indirectly  by  the  changes  in  the  forms  of  life  with  which 
it  has  been  associated.  Migration  brings  a  species  into 
relation  with  a  different  set  of  other  species,  which  may 
furnish  it  with  food,  or  become  its  rivals  or  enemies. 

Lost  Groups  do  not  reappear.  —  As  a  general  rule,  a 
species,  or  a  more  comprehensive  group,  which  has  once 
become  extinct,  does  not  reappear.  To  this  proposition 
there  are  some  curious  apparent  exceptions.  A  few  land 
Snails  are  found  in  the  Carboniferous,  but  no  land  Snails 
have  been  recognized  from  the  Permian,  Triassic,  or  Ju- 
rassic formations.  In  the  Cretaceous  they  reappear,  and 
from  that  time  the  series  is  substantially  continuous.  A 
few  Scorpions  are  found  in  the  Upper  Silurian ;  none 
have  been  recognized  from  the  Devonian  ;  but  in  the 
Carboniferous  both  Scorpions  and  Spiders  occur.  Both 
these  groups  appear  to  be  missing  from  the  Permian  and 
from  the  whole  series  of  Mesozoic  strata.  They  reappear 
in  the  Tertiary.  Amphibians  of  the  order  Labyrintho- 
donts  appear  in  the  Subcarboniferous  (or,  probably,  in 
the  Devonian),  and  continue  through  the  Triassic,  possi- 
bly into  the  beginning  of  the  Jurassic.  The  class  of 
Amphibians  then  remains  unrepresented  until  a  Salaman- 
der appears  in  the  Lower  Cretaceous.  Such  exceptions, 


460  HISTORICAL   GEOLOGY. 

however,  are  readily  explained  as  due  to  the  imperfec- 
tion of  the  record.  They  are  not  sufficient  to  throw  any 
doubt  upon  the  general  principle. 

Persistence  of  Character  of  Faunas.  —  In  the  early  periods 
of  the  earth's  history  there  appears  to  have  been  little 
differentiation  between  the  faunas  and  floras  of  various 
continents.  After  the  development  of  such  differentia- 
tion, and  the  acquisition  of  distinct  faunal  characteristics 
by  the  various  continents,  there  is  a  noteworthy  tendency 
for  these  characteristics  to  persist  from  one  geological 
period  to  another.  That  principle  is  strikingly  illustrated 
in  the  comparison  of  the  Mammalian  faunas  of  the  Quater- 
nary with  the  existing  faunas.  In  the  early  Quaternary, 
Australia  was  distinctively  the  land  of  Marsupials,  and, 
in  somewhat  less  striking  degree,  South  America  was  the 
land  of  Edentates.  The  present  Mammalian  faunas  of 
those  regions  are  characterized  by  the  predominance  of 
the  same  types. 

Missing  Links.  —  The  general  laws  of  succession  of 
organic  life,  as  above  formulated,  are  all  obviously  in 
accord  with  the  theory  of  evolution.  Yet  there  are  pale- 
ontological  facts  whose  bearing  appears,  prima  facie, 
adverse  to  that  doctrine.  According  to  the  theory  of 
evolution,  existing  species  ought,  in  most  cases,  to  be  well 
denned,  since,  in  general,  a  species  now  existing  must  be 
supposed  to  have  been  derived,  not  from  some  other  exist- 
ing species,  but  from  a  species  now  extinct.  Between  the 
ancestral  and  the  derived  species  there  must  have  been 
sometime  a  series  of  more  or  less  finely  gradational  forms. 
How  fine  those  gradations  must  have  been,  depends  some- 
what upon  the  method  of  evolution.  If  evolution  was  by 
the  accumulation  of  minute  and  imperceptible  variations, 
the  series  must  have  presented  very  fine  gradations.  If, 
as  is  probable,  occasional  abrupt  variations  have  played 
a  considerable  r61e,  the  gradations  would  have  been  less 
fine.  On  that  supposition,  the  missing  links  may  be  miss- 
ing because  they  never  existed.  Certain  it  is  that  in  most 


PROGRESS  OF  LIFE.  461 

cases  fine  gradations  between  fossil  species  are  no  more  to 
be  found  than  between  living  species.  In  the  great  majority 
of  cases,  fossil  species  are  well  denned.  Moreover,  more 
comprehensive  groups  often  appear  in  geological  history 
where  no  preexistent  forms  are  known  as  probable  ances- 
tors for  them ;  and  the  order  of  introduction  of  related 
groups  is  often  different  from  that  which  would  be  pre- 
dicted, a  priori,  on  the  basis  of  the  theory  of  evolution. 
The  highly  diversified  fauna  of  the  Cambrian  includes 
many  groups  of  by  no  means  very  low  grade,  which  appear 
without  any  apparent  ancestry.  Hexapod  Insects  appear 
in  the  Lower  Silurian,  while  the  Myriopods,  which  are 
more  generalized,  and  would  seem  to  be  a  more  primitive 
group,  are  unknown  until  the  Devonian.  No  fossil  forms 
have  been  discovered  which  can  be  imagined  to  be  the 
immediate  ancestors  of  the  Placoderms,  Selachians,  and 
Ganoids  of  the  Lower  Silurian.  No  intermediate  forms 
have  been  discovered  bridging  the  gap  between  Seaweeds 
and  Acrogens.  The  sudden  appearance  of  numerous 
orders  of  Placental  Mammals  in  the  very  earliest  Eocene 
is  at  least  startling.  The  interrupted  chronological  range 
of  several  groups,  as  in  the  cases  of  Snails,  Arachnoids, 
and  Amphibians,  above  mentioned,  would  be  a  fatal  objec- 
tion to  the  theory  of  evolution,  if  the  interruptions  were 
believed  to  be  other  than  merely  apparent.  So  long  as 
the  complete  change  in  the  life  of  the  globe  at  the  close 
of  the  Paleozoic,  and  again  at  the  close  of  the  Mesozoic, 
was  believed  to  be  due  to  universal  extermination,  the 
theory  of  evolution  could  have  no  standing  ground. 

The  Imperfection  of  the  Geological  Record.  —  This 
phrase,  now  become  classical,  expresses  the  substance  of 
the  answer  given  by  Darwin,  and  by  all  evolutionists,  to 
such  difficulties  as  have  just  been  cited.  The  bearing  of 
the  principle  on  some  special  cases  has  already  been  dis- 
cussed (pages  251,  288,  289).  But  the  subject  of  the 
imperfection  of  the  geological  record  may  well  receive 
some  further  comment. 


462  HISTOKICAL  GEOLOGY. 

1.  Geological  Conditions  of  Imperfection  of  the  Record.— 
Fossiliferous  strata  of  considerable  thickness  can  be  formed 
only  during  a  progressive  subsidence ;  but,  in  general, 
relative  elevation  must  have  predominated  over  subsidence 
in  the  history  of  the  continents  ;  and,  moreover,  Darwin  is 
probably  correct  in  maintaining  that  periods  of  elevation 
have  been  more  fruitful  in  evolutionary  changes  than 
periods  of  subsidence.  After  fossiliferous  strata"  have 
been  formed,  their  record  has  often  been  obliterated  by 
nietamorpliism.  Fossiliferous  strata  not  of  great  thick- 
ness may^  often  be  entirely  removed  by  erosion.  The  vast 
areas  occupied  by  plutonic  and  metamorphic  rocks  afford 
striking  proof  of  the  enormous  denudation  which  has  taken 
place,  since  these  rocks  must  have  assumed  their  present 
crystalline  character  under  the  pressure  of  hundreds  or 
thousands  of  feet  of  superincumbent  rock.  In  no  region 
of  the  globe  have  we  any  continuous  series  of  fossiliferous 
strata,  and  in  many  districts  only  mere  fragments  of  the 
series  are  present.  The  most  abrupt  changes  in  the  fossil 
contents  of  strata  usually  occur  where  the  strata  are  un- 
conformable  ;  and  unconformability,  as  explained  on  page 
57,  is  always  the  sign  of  a  lost  interval  in  the  record.  It 
must,  moreover,  be  considered  that  the  period  whose  record 
is  lost  by  unconformability  is  necessarily  a  period  of  geo- 
graphical change  for  the  region  in  question.  The  area 
which  had  been  receiving  sediment  has  been  elevated  so 
as  to  become  dry  land,  and,  after  a  longer  or  shorter 
period  of  erosion,  has  been  again  depressed  below  the 
water  level.  These  times  of  geographical,  and  conse- 
quently of  climatic,  change,  are  the  times  in  which  evolu- 
tionary changes  in  the  fauna  and  flora  are  necessarily  most 
rapid.  The  geological  record  is  therefore  defective  by 
the  loss  of  those  chapters  which,  if  present,  would  afford 
the  history  of  the  most  critical  periods.  The  great  changes 
in  fauna  and  flora  at  the  close  of  the  Paleozoic  and  the 
Mesozoic  are  thus  naturally  correlated  with  the  great 
geographical  revolutions  which  occurred  at  those  times. 


PKOGHESS   OF   LIFE.  463 

2.  Biological  Conditions  of  Imperfection  of  the  Record.  — 
The  vast  majority  of  living  beings  die  under  such  circum- 
stances that  there  is  no  chance  of  their  fossilization.  In 
order  that  we  may  have  a  fossil  for  study,  it  is  necessary 
that  the  entire  organism,  or  some  recognizable  part  of  it, 
should  be  buried,  before  it  can  be  decomposed  or  dissolved 
(or  at  least  an  impression  of  the  organism  made),  in  some 
deposit  which  is  subsequently  preserved  without  too  much 
alteration,  and  brought  into  an  accessible  position.  Only 
under  an  exceptional  combination  of  circumstances  can 
this  be  the  fate  of  an  individual  plant  or  animal.  The 
chance  of  such  preservation  is  greater  in  the  case  of 
aquatic,  than  in  that  of  terrestrial,  animals  and  plants. 
It  would  naturally  be  expected,  therefore,  that  the  record  of 
terrestrial  life  would  be  extremely  ragged.  Moreover,  in 
general,  only  somewhat  indurated  structures,  or  skeletons, 
can  be  expected  to  be  preserved.  Terrestrial  plants  whose 
tissues  contain  no  woody  fiber,  and  animals  that  are 
destitute  of  skeleton,  have  but  an  infinitesimal  chance  of 
leaving  any  record.  This  latter  principle  probably  affords 
the  chief  explanation  of  the  mystery  of  the  Cambrian 
fauna  (page  251),  although  it  must  also  be  remembered 
that  the  Archaean  rocks  have  suffered  so  extensive  meta- 
morphism  that  whatever  fossils  they  may  have  contained 
are  likely  to  have  been  obliterated,  and  that  the  universal 
unconformability  between  the  Archaean  and  the^  Cambrian 
shows  a  lost  interval  in  the  record  during  which  evolu- 
tionary changes  may  have  been  in  progress. 

That  the  geological  record  is  extremely  imperfect,  is 
illustrated  by  the  well-known  fact  that  multitudes  of 
fossil  species  are  known  as  yet  only  by  a  single  specimen. 
In  many  cases  a  family,  an  order,  or  a  class,  in  some 
particular  formation,  may  be  represented  by  only  one  or 
two  specimens.  In  the  Jurassic  formation  of  Europe, 
the  class  of  Birds  is  represented  by  two  somewhat  im- 
perfect skeletons  and  a  single  odd  feather.  In  the 
Jurassic  of  North  America,  the  same  class  is  represented 


464  HISTORICAL   GEOLOGY. 

by  a  single  doubtful  fragment  of  a  skull  (page  345).  In  the 
Triassic  of  North  America,  the  class  of  Mammals  is  repre- 
sented by  two  lower  jaws.  There  can  be  no  reasonable  doubt 
that  the  imperfection  of  the  geological  record  affords  a 
sufficient  answer  to  all  arguments  against  evolution  based 
upon  the  gaps  that  exist  in  the  series  of  fossils.  Negative 
evidence  in  paleontology  must  be  considered  of  very  little 
value. 

CONCLUSION. 

In  spite  of  all  difficulties  and  uncertainties,  geology  is 
able  thus  to  give  in  outline  the  history  of  the  evolution 
of  Man  himself  and  of  his  dwelling  place.  It  shows 
how  the  featureless  simplicity  of  the  molten  globe  has 
given  place  to  continent  and  ocean,  mountain  and  valley, 
plain  and  plateau,  river  and  lake,  cataract  and  glacier ; 
how  ores  have  been  stored  in  veins,  and  coal  accumu- 
lated in  strata,  and  rock  material  crystallized  into  granite 
strength  and  gemlike  beauty.  It  shows  how  the  earth 
has  come  to  be  a  fit  dwelling  place  for  a  creature  of 
such  physical  and  spiritual  needs  and  capacities  as  those 
of  Man ;  and  how,  in  the  progress  of  life,  those  plants 
and  animals  have  been  evolved  which  could  minister 
to  Man's  physical  or  mental  life.  It  shows  how  the 
upward  progress,  from  Protozoan  simplicity,  through  Fish 
and  Amphibian  and  Reptile  and  Mammal,  has  culminated 
at  last  in  Man  himself,  the  crown  of  creation,  sharing 
with  the  animal  kingdom  a  place  in  nature,  but  asserting 
by  his  intellectual  and  spiritual  endowments  a  place  above 
nature.  While  it  is  the  work  of  science  to  trace  the 
method  of  this  twofold  evolution,  science,  as  such,  knows 
nothing  of  efficient  cause  or  of  purpose ;  but  it  leaves 
full  scope  for  faith  that  the  Power,  whose  modes  of  work- 
ing science  may  in  part  reveal,  is  intelligent  and  personal, 
and  that  the  whole  process  of  the  evolution  of  Man  and 
his  dwelling  place  has  been  guided  by  infinite  Wisdom  to 
the  fulfillment  of  a  purpose  of  infinite  Love. 


INDEX. 


NOTE.  —  The  asterisk  after  the  number  of  a  page  indicates  that  the  subject  referred  to 
is  illustrated  by  a  figure. 


Abyssal  deposits,  92. 

Acadian  period,  244. 

Acadian  range,  327. 

Acids,  organic,  geological  effect  of,  113. 

Aconcagua,  177. 

Acrodus,  82*. 

Acrogens,  88. 

Age  of,  229,  290. 

Carboniferous,  300*,  301. 

Cretaceous,  367. 

Devonian,  279*. 

Jurassic.  336. 

Lower  Silurian,  254*. 

relation  of,  to  evolution,  288. 

Triassic.  336,  337*,  338. 

Upper  Silurian,  270. 
Acrostichites,  337*,  388. 
Acrotreta,  247*. 
Actinia,  66*. 
Actinocrinus,  304*. 
Actinocyclus,  392*. 
Actlnoptychus,  8S*,  392*. 
^olian  denudation,  118,  119*. 
^Eolian  deposits,  120,  121*. 
.iEons,  geological,  227. 
^Epyornis,  extinction  of,  441. 
Agassiz,  Lake,  424. 
Age  of  strata,  how  determined,  228. 
Ages,  geological,  227. 
Agnostus,  322. 
Albirupian  stage,  864. 
Albite,  20. 
Alcyoniarians,  66*. 
Alga-,  87,  88*. 

Cambrian,  245. 

Cretaceous,  367. 

Devonian,  279. 
Lower  Silurian,  254. 
siliceous  deposits  made  by,  106. 
Upper  Silurian,  268. 
Alkaline  lakes,  117. 
Alluvial  deposits,  188. 


Alps,  elevation  of;  403. 

glaciers  in,  159,  161*,  164. 
Altitude,  effect  of,  on  temperature,  168. 
Alum  clays,  112. 
Alum  shale,  35. 
Amazon  Kiver,  125,  150. 
Amber,  99. 

Insects  in,  393. 
Ambonychia,  256*. 
America.  See  North  America,  South 

America. 

Ammonites,  347*,  348*,  370,  371*. 
Amphibians,  84. 

Age  of,  229,  290. 

Carboniferous,  306,  308*. 

Devonian,  286. 

interrupted  range  of,  in  time,  459. 

Jurassic,  351. 

Tertiary,  394. 

Triassic,  339,  340*,  341*,  351,  352*. 
Amphilestes,  358*. 
Amphioxus,  81. 
Amygdaloid,  188. 
Anatifa,  77*. 
Anchisaurus,  342*. 
Anchitherium,  399*,  400. 
Anchura,  74*. 
Andalusite,  22*. 
Andesine,  20. 
Andesite,  38,  175. 
Angiosperms,  90*. 

Cretaceous,  367*. 

Tertiary,  390,  391*. 

Animal  and  plant,  distinctions  between,  68. 
Animal  kingdom,  59. 
Anisichnns,  340*. 
Anomoepus,  340*. 
Anoplotherium,  398. 
Antecedent  drainage,  142. 
Anthozoans,  65,  66*. 

Cambrian,  246*. 

Carboniferous,  303,  804*. 


465 


466 


EffDEX. 


Cretaceous,  868. 

Devonian,  282*. 

Jurassic,  345,  846*. 

Lower  Silurian,  255,  256*. 

Upper  Silurian,  269*,  270. 
Anthracite,  25,  214,  298. 

origin  of,  192,  214. 

vegetable  tissues  in,  309,  810*. 
Anthracite  region  of  Pennsylvania,  214,  292*. 
Anthracopalaemon,  805*. 
Anticlinal  axis,  53*,  54. 
Anticline,  53*,  54. 
Anticlines,  erosion  of,  136*,  218. 
Anticlinoriuin,  220. 
Apatite,  105. 

Appalachian  range,  211,  826. 
Appalachian  region,  folds  in,  211,  212*,  213*. 

thickness  of  strata  in,  211,  317,  825. 
Appalachian  revolution,  325. 
Appalachian  system,  326. 
Aquatic    organisms,     the    principal     rock- 
makers,  98. 
Arachnoids,  79. 

Carboniferous,  805*,  306*. 

interrupted  range  of,  in  time,  459. 

Upper  Silurian,  272. 
Araucaria,  90*. 
Archaean  rocks,  origin  of,  289. 
Archaean  time,  227,  236. 
Archaean  V,  237,  446. 
Archaeocyathus,  246*. 
Archaeoniscus,  350*. 
Archseopteris,  279*. 
Archaeopteryx,  356,  857*. 
Archimedes,  303,  304*. 
Arctic  coal  areas,  293. 
Arenicola.    See  Lobworm. 
Arenig  group,  252,  253. 
Argillite.    See  Slate. 
Artesian  wells,  145*. 
Arthrolycosa,  306*. 
Arthropods,  76,  77*. 

Cambrian,  248*,  249*. 

Carboniferous,  805*,  806*. 

Devonian,  281,  282,  283*. 

Jurassic.  350*. 

Lower  Silurian,  256*,  257,  258*. 

Tertiary,  893. 

Triassic,  338,  339*,  850*. 

Upper  Silurian,  269*,  270,  271*. 
Arthrostracans,  77*,  78. 
Articulates,  60. 
Asaphus,  256*.  257,  822. 
Asbestus,  21. 

Ascidians.    See  Tunicates. 
Ashes,  volcanic,  175. 
Aspidorhynchus,  84*. 
Asterioids,  68*,  69. 

Jurassic,  346. 


Lower  Silurian,  256. 

Triassic,  346. 

Upper  Silurian,  68*,  270. 
Athyris,  71*,  304*. 

Atlantic  Border  geanticline,  262,  876. 
Atlantic  coast  of  North  America,  changes  of 

level  in,  429. 
Atlantosaurus,  343. 
Atlantosaurus  beds,  334. 
Atmosphere,  chemical  action  of,  111. 

mechanical  action  of,  118. 
Atmospheric  absorption,  effect  of,  on  tem- 
perature, 168. 
Atolls,  102*,  103*,  104*. 
Atrypa,  71*,  283*. 
Auk,  great,  extinction  of,  442. 
Australia,    Marsupials    of,    in    Quaternary, 

434. 
Avicula,  269*. 

range  of,  in  time,  259. 
Axial  plane  of  fold,  53*. 
Axis,  anticlinal,  53*,  54. 

synclinal,  53*,  55. 
Azoic.    See  Archaean. 

Bacillaria,  88*. 
Baculites,  370,  371*. 
Bala  formation,  252,  254. 
Baptanodon  beds,  884. 
Barite,  198. 
Barnacles,  77*,  78. 
Barrier  reefs,  102*. 

theory  of,  103,  104*. 
Basalt,  39,  175. 
Base  level,  140. 
Bathyactis,  92. 

Bathymetric  map  of  oceans,  10*,  11*. 
Bathyurus,  322. 
Bats,  Tertiary,  394,  398,  400. 
Beach  formations,  152,  153*,  154. 
Bear,  cave,  431. 
Beehive  Geyser,  185,  186*. 
Beetles,  Carboniferous,  306. 
Belemnitella,  371*. 
Belemnites,  348,  849*,  870,  871*. 
Belemnoteuthis,  349*. 
Bilin,  diatomaceous  deposit  of,  392. 
Biotite,  20. 
Bird  tracks,  so-called,  of  Connecticut  Valley, 

341*. 
Birds,  85. 

Cretaceous,  874,  375*,  877*. 

Jurassic,  345,  356,  357*. 

Tertiary,  394. 
Bird's-eye  Limestone,  253. 
Bituminous  coal,  25,  298. 
Black  Hills  of  Dakota,  184,  834. 
Black  River  Limestone,  253. 
Black  Shale,  Devonian,  278. 


INDEX. 


467 


Blastoids,  67*,  68. 

Carboniferous,  303,  304*. 
Bog  iron  ore,  116. 
Bonneville,  Lake,  425. 
Bore,  150. 
Bowlder  clay,  406. 

Bowlders,  glacial,  large  size  of,  162,  406. 
Brachiate  Crinoids,  67*,  68*. 
Brachiopods,  70,  71*. 

Cambrian,  247*. 

Carboniferous,  303,  304*. 

Devonian,  281,  282,  283*. 

Jurassic,  346,  347*. 

Lower  Silurian,  256*,  257. 

Triassic,  346. 

Upper  Silurian,  269*,  270,  271*. 
Brachyurans,  77*,  79. 
Brains  of  Tertiary  Mammals,  396,  397*. 
Brandon,  fossil  fruits  of,  389,  391*. 
Breccia,  34. 
Brontosaurus,  343*. 
Brontozoum,  341*. 
Bronze  Age,  436. 
Brown  coal,  25. 
Bryophytes,  88. 
Bryozoans,  70*. 

Carboniferous,  803,  804*. 

Lower  Silurian,  256*. 
Buffalo,  extinction  of,  442. 
Buhrstone,  389. 
Bulla,  74*. 

Bunter  Sandstein,  334. 
Buprestis,  350*. 

Caerfai  group,  230. 

Calamites,  280,  300*,  302. 

Calamopsis,  391*. 

Calaveras  skull,  439. 

Calcareous  rocks.  32,  40,  99. 

Calciferous  Sandrock,  253. 

Calcite,  23*,  198. 

Calcium  bicarbonate,  115. 

Calcium  carbonate.    See  Calcite. 

California,  lava  sheets  of,  189. 

Callocystites,  67*. 

Cambrian  era,  228,  244. 

Cambrian  fauna,  relation  of,  to  evolution,  251 

463. 

Camptosaurus,  343*. 
Canada,  geological  map  of,  235*. 
Canadian  period,  252. 
Cancer,  77*. 
Cannel  coal,  25. 
Canons,  133. 
Caradoc  group,  252,  254. 
Carbon  and  its  compounds,  18,  24. 
Carbon  dioxide,  geological  action  of,  118. 
Carbonaceous  formations,  107. 
Carbonic  acid.    See  Carbon  dioxide. 


Carboniferous  era,  229,  290. 

Carboniferous  period,  291,  296,  814. 

Carcharodon,  82*,  394*. 

Carnivores,  Tertiary,  394,  396,  398,  400,  402. 

Carpathians,  elevation  of,  403,  404. 

Carpolithes,  391*. 

Jarterella,  63*. 

Oaryocrinus,  269*. 

Cascade  Range,  362. 

Cascades,  182. 

Catopterus,  339*. 

Catskill  formation,  277. 

Catskill  Mountains,  218. 

Cauda-galli  Grit,  276. 

Cave  animals  of  Quaternary,  480. 

Caverns,  143*. 

Cenozoic  time,  228,  385. 

Cephalaspis,  284,  285*. 

Cephalization,  progress  in,  458. 

Cephalopods,  74,  75*. 

Cambrian,  247. 

Carboniferous,  304. 

Cretaceous,  370,  371*. 

Devonian,  281,  282,  283*. 

Jurassic,  347*,  349*. 

Lower  Silurian,  256*,  257. 

Triassic,  347,  348*. 
Ceratodus,  351. 
Ceratopsidae,  372*. 
Cervus  euryceros,  481. 
Cestracion,  82*. 

Cestracionts,  82*,  284,  828,  850. 
Cetiosaurus,  854. 
Chaetetes,  257. 
Chain  coral.    See  Halysites. 
Chalcedony,  19. 
Chalk,  32,  40,  365,  366. 
Chainplain,  Lake,  condition  of,  in  Quaternary, 

421,  424. 
Chatnplain  period,  405,  420. 

marine  deposits  of,  421. 

river  deposits  of,  422. 
Changes  of  level,  modern,  427. 
Chazy  Limestone,  253. 
Cheirolepis,  84*. 

Chemical  action,  as  a  source  of  heat,  171. 
Chemical  action  of  atmosphere,  111. 
Chemical  action  of  water,  111,  187,  193, 198, 

236. 

Cheinung  epoch,  277. 
Chemung  period,  277. 
Chert,  36,  107. 
Chiastolite,  22. 

Chile,  recent  changes  of  level  in,  428. 
Chirotherium,  852*. 
Chlorides,  26. 
Chlorite,  21. 
Chlorite  schist,  89. 
Chonetes,  283*,  804*, 


468 


INDEX. 


Chrysalidina,  61*,  368*. 

Chrysolite,  21. 

CidariS,  346*. 

Cimoliosaurus,  372. 

Cincinnati  Island,  263,  287. 

Cincinnati  uplift,  220,  263. 

Cinders,  volcanic,  175. 

Cinnamomura,  891*. 

Circumdenndation,  mountains  of,  138. 

Cirques,  131. 

Cirripeds,  77*,  78. 

Cladiscites,  848*. 

Clam,  fossil,  in  Miocene,  898. 

Clathropteris,  837*,  888. 

Clay,  34. 

alum,  112. 

Bowlder,  406. 

of  ocean  bottom,  92. 

Weald,  366. 

Clay  ironstone,  28,  297. 
Clay  slate.    See  Slate. 
Cleavage,  crystalline,  19. 

slaty,  81.  48*,  219. 
Cleodora,  74*. 
Cleveland  Shale,  278. 
Climate,  causes  of  changes  in,  167. 

Carboniferous,  312. 

Champlain,  434. 

Cretaceous,  878. 

Glacial,  cause  of,  418. 

Jurassic,  361. 

Paleozoic,  821. 

Tertiary,  404. 
Clinometer,  52*. 
Clinton  epoch,  266,  273. 
Club  mosses.    See  Lycopods. 
Coal,  24. 

bituminous,  25. 

brown,  25. 

cannel,  25. 

Carboniferous,  292,  296,  298. 

Cretaceous,  365. 

impurities  in,  311. 

lamination  of,  298. 

origin  of,  309. 

Tertiary,  389. 

Triassic,  333. 

vegetable  tissues  in,  809,  310*. 
Coal  areas  of  Europe,  293,  295*. 
Coal  areas  of  North  America,  292*. 
Coal  areas  of  Pennsylvania,  map  of,  292*. 
Coal  Measures,  296. 
Coccosteus,  284,  285*. 
Cockroaches,  Lower  Silurian,  258. 
Ccelenterates,  64,  65*,  66*. 

Cambrian,  246*. 

Carboniferous,  303,  304*. 

Cretaceous,  368. 

Devonian,  282*. 


Jurassic,  345,  846*. 

Lower  Silurian,  254,  255*,  256*. 

Upper  Silurian,  269*,  270. 
Coin  conglomerate,  440*. 
Colorado  epoch,  365. 
Colorado  River,  canon  of,  42,  43*,  132*,  188, 

134*. 

Columbia  River,  lava  sheet  of,  189. 
Columnar  structure,  173*. 
Comanche  series,  365. 
Comprehensive  types,  455. 
Compsognathus,  354. 
Concretions,  46*,  47*. 
Conformable  strata,  56. 
Conglomerate,  34. 

Oneida,  266,  273. 

Pottsville,  296. 
Conifers,  90*. 

Carboniferous,  302. 

Cretaceous,  367. 

Devonian,  281. 

Jurassic,  336. 

Triassic,  336,  338. 
Connecticut  River,  deposits  at  mouth  of,  150. 

terraces  of,  426*. 
Connecticut  Valley,  sandstones  of,  332,  859. 

trap  rocks  of,  189,  359. 
Conodonts,  248. 
Consequent  drainage,  142. 
Contemporaneous    sheets  of  igneous  rock, 

188. 

Continent  and  ocean,  boundary  of,  12. 
Continental  plateaus,  7. 
Continents,  general  relief  of,  14. 

height  of,  8. 

origin  of,  206. 
Contraction    and    expansion   of   rocks,    by 

changes  of  temperature,  172. 
Contraction     theory    of    mountain-making, 

207. 

Coprolites,  106,  356. 
Coral  animals.    See  Anthozoans,  Bryozoans, 

Hydrozoans. 

Coral  islands,  102*,  103*,  104* 
Coral  reefs,  100,  102*,  104*. 
Corallines,  88. 

Corals,  reef-forming,  range  of,  95. 
Cordilleras,  210. 
2orniferous  period,  275,  276. 
Coscinodiscus,  392*. 
Cosmoceras,  347*. 

rabs,  77*,  78. 

Crania,  range  of,  in  time,  259. 
iraters,  174. 
Creodonts,  396,  400. 
retaceous  era,  231,  331,  362. 

map  of  North  America  in,  364*. 
Crevasses,  159,  160*. 
>inoidal  Limestone,  294. 


INDEX. 


469 


Crinoids,  67*,  68*. 

Cambrian,  246. 

Carboniferous,  303,  304*. 

Jurassic,  346. 

Lower  Silurian,  256*. 

Triassic,  346*. 

Upper  Silurian,  269*,  270. 
Crocodiles,  85. 

Cretaceous,  374,  388. 

Jurassic,  340,  354. 

Triassic,  340,  354. 
Crocodilus,  388. 
Cross-bedded  structure,  155*. 
Crustaceans,  77*. 

Cambrian,  248*,  249*. 

Carboniferous,  305*. 

Devonian,  281,  282,  283*. 

Jurassic,  350*. 

Lower  Silurian,  257,  258*. 

Triassic,  338,  339*,  350*. 

Upper  Silurian,  269*,  270,  271*. 
Cryptogams,  86,  88*. 

Crystalline  rocks,  28,  29,  35,  41, 175,  188, 191. 
Ctenacanthus,  307*. 
Ctenoid  scales,  84*. 
Cumberland  Mountains,  218. 
Cuneolina,  61*,  368*. 
Currents,  oceanic,  150. 

tidal,  149. 

wind-made,  150. 
Cuttlefish,  76. 
Cyanite,  22. 
Cyathophylloids,  66. 

Devonian,  282*. 

Lower  Silurian,  255,  256*. 

Upper  Silurian,  269*,  270. 
Cyathophyllum,  282*. 
Cycads,  90,  336*. 

Carboniferous,  302. 

Cretaceous,  368. 

Devonian,  281. 

Jurassic,  336,  337*. 

Triassic,  336,  337*. 
Cycas,  336*. 
Cycloid  scales,  84*. 
Cyclonema,  269*. 
Cyprina,  72*. 
Cyrtoceras,  248. 
Cystoids,  67*,  269*,  270. 
Cythere,  77*. 

Dakota  epoch,  365. 
Dapedius,  351*. 
Decapitated  folds,  56*. 
Decapods,  77*,  78. 

Carboniferous,  305*. 

Devonian,  281. 

Jurassic,  850. 

Triassic,  350*. 


Deccan,  lava  sheet  of,  189. 

Deep-sea  life,  characteristic  types  of,  94. 

Deer,  Irish,  431. 

Degradation,  means  of,  165. 

Deltas,  139*. 

Dendrophyllia,  66*. 

Dent  de  Morcles,  54*. 

Denudation.    See  Erosion. 

Deposits,  ajolian,  120,  121*. 

estuarine,  139. 

fluvial,  138,  166. 

fluvio-marine,  153. 

glacial,  163,  167,  406. 

marine,  152,  166. 
Depth/range  of  life  in,  91. 
Desmids,  88,  368. 
Devonian  era,  229,  275. 
Diabase.    See  Dolerite. 
Diamond,  24. 

Diatomaceous  deposits,  106,  109,  891,  892*. 
Diatomaceous  ooze,  92. 
Diatoms,  88*. 

Carboniferous,  supposed  to  be  identical 
with  living  species,  328. 

Cretaceous,  368. 

Devonian,  279. 

Tertiary,  391,  392*. 
Dibranchs,  75*. 

Cretaceous,  370,  871*. 

Jurassic,  348,  349*. 

Triassic,  348. 
Dicotyledons,  90*,  91. 
Dictyocha,  392*. 
Dikes,  188,  196. 
Dinichthys,  284,  285*. 
Dinoceras,  397*,  398*,  399. 
Dinornis,  extinction  of,  441. 
Dinosaurs,  Cretaceous,  372*. 

Jurassic.  340,  342,  343*,  344*,  854. 

Triassic,  340*,  341*,  842*,  854. 
Diuotherium,  401*. 
Diorite,  38,  188. 
Dip,  51*. 

Diphycercal  tails,  81. 
Diplograptus,  255*. 
Dipnoans,  84. 

Carboniferous,  306. 

Devonian,  284,  286*. 

Jurassic,  339,  350,  851. 

Triassic,  339,  350,  351. 
Diprotodon,  434. 
Dipters,  79. 
Dipterus,  286*. 

Discina,  range  of,  in  time,  259. 
Dislocations  of  strata,  50. 
Distribution  of  marine  life,  causes  limiting, 

93. 

Diversification  of  type,  progress  in,  455. 
Dodo,  extinction  of,  441. 


470 


INDEX. 


Dolerite,  39,  188. 
Dolomite,  23. 
Domes,  trachytic,  184. 
Drainage,  antecedent,  consequent,  and  super- 
imposed, 142. 
Drift,  406. 

area  of,  411. 

direction  of  movement  of,  411. 

origin  of,  408. 
Dripstone,  40. 
Dromatherium,  345*. 
Druinlins,  417. 
Duckbill,  86. 
Dudley  Limestone,  268. 
Dunes,  121*. 

Dust,  transportation  of,  by  wind,  122. 
Dykes.    See  Dikes. 
Dynamic  metamorphism,  195. 
Dynamical  geology,  6,  97. 

Eager,  150. 

Earth,  interior  of,  solid  or  liquid,  204. 

internal  heat  of,  170. 

size  and  form  of,  7. 

system  in  features  of,  14. 
Earthquakes,  204. 

in  connection  with  volcanoes,  181, 182, 184. 
Earthworms,  geological  action  of,  110. 
East  Rock,  333. 
East  Tennessee,  valley  of,  218. 
Eccentricity  of  earth's  orbit,  169. 
Echidna,  86. 
Echinoderms,  66,  67*,  68*. 

Cambrian,  246. 

Carboniferous,  303,  304*. 

Cretaceous,  369. 

Jurassic,  346*. 

Lower  Silurian,  255,  256*. 

Triassic,  846*. 

Upper  Silurian,  269*,  270. 
Echinoids,  68*,  69. 

Cretaceous,  369. 

Jurassic,  846*. 

Triassic,  346. 
Echinus,  68*. 
Edentates.  Quaternary,  432,  433*,  434*. 

Tertiary,  395,  402. 
Edestosaurus,  373*. 
Elasmobranchs.    See  Selachians. 
Elasmosaurus,  372. 
Elephants,  Quaternary,  431. 

Tertiary,  401. 

Elephas  priinigenius.    See  Mammoth. 
Elevation,  effect  of,  on  temperature,  168. 
Embryology  and    paleontology,  parallelism 

of,  454. 

Enaliosaurs.  352,  358*. 
Encrinus,  67*. 
Endogenous  stems,  89,  90*. 


Engis  skull,  437. 

England,  geological  map  of,  295*. 

Entomostracans,  77*,  78. 

Eocene  period,  386. 

Eopaleozoic  section,  229,  243,  244. 

Eoscorpius,  305*. 

Eozoon,  241*. 

Epochs,  geological,  232. 

Equiseta,  89. 

Carboniferous,  300*,  302. 

Devonian,  280. 

Jurassic,  336. 

Triassic,  336. 
Equus,  397*,  399*. 
Eras,  geological,  228. 
Erie  Shale,  278. 
Erosion,  by  glaciers,  168. 

by  ocean  waves,  147,  148*. 

by  rain,  128. 

by  rivers,  126. 

by  wind,  118,  119*. 

effect  of,  on  folded  rocks,  55,  56*. 

topographical  forms  resulting  from,  135*, 

136*. 
Eruptions,  Cambrian,  245. 

Cretaceous,  189,  384. 

from  fissures,  187. 

in  Connecticut  Valley,  333,  359. 

in  connection  with  mountain-making,  221. 

in  Deccan,  189,  384. 

in  Lake  Superior  region,  245. 

in  northwestern  United  States,  189,  404. 

submarine,  184. 

Tertiary,  189,  404. 

Triassic,  333,  359. 

volcanic,  174. 
Eschara,  70*. 
Eskers,  417. 
Estheria,  338,  839*. 
Estuary  formations,  189. 
Etna,  177,  184. 
Etoblattina,  306*. 
Eucyrtidium,  68*. 
Eurypterids,  79,  271*. 
Eurypterus,  271*. 
Evolution,  232,  251,  288,  858,  450. 
Exogenous  steins,  89,  90*. 
Expansion   and    contraction   of   rocks,   by 

changes  of  temperature,  172. 
Extinct  groups  do  not  reappear,  459. 
Extinction  of  species,  causes  of,  330,  385, 
458. 

in  modern  times,  441. 
Extrusive  sheets  of  igneous  rock,  188. 
Eyes  of  deep-sea  animals,  94. 

Fagus,  391*. 
False  veins,  203. 
Fasciolaria,  371*. 


INDEX. 


471 


Faults,  53*,  211,  213*. 
Favosites,  269*,  270,  282*. 
Feldspar,  20. 

decomposition  of,  118. 
Felsite,  38,  188. 
Ferns,  88. 

Carboniferous,  300*,  301. 

Cretaceous,  367. 

Devonian,  279*,  280. 

Jurassic,  336. 

Triassic,  336,  337*,  338. 
Fingal's  Cave,  173,  190. 
Fiords,  419. 
Firn,  159. 
Fishes,  81,  82*,  83*,  84*. 

Age  of,  229,  263. 

Carboniferous,  306,  307*. 

Cretaceous,  370,  372*. 

Devonian,  283,  284*,  285*,  286*. 

Jurassic,  339,  350,  851*. 

Lower  Silurian,  258. 

relation  of,  to  evolution,  289. 

Tertiary,  393,  394*. 

Triassic,  339*,  350. 

Upper  Silurian,  272. 
Fissure  eruptions,  187. 
Flabellina,  61*,  368*. 
Flags,  31. 
Flagstone,  31. 
Flies,  79. 
Flint,  19,  107,  366. 

implements  of,  436. 
Flood  plains,  131. 
Floridian  formation,  388. 
Flow-and-plunge  structure,  155, 156*. 
Flowering  plants.    See  Phanerogams. 
Flowerless  plants.    See  Cryptogams. 
Fluorite,  198. 

Fluvio-inarine  formations,  153. 
Fold,  axial  plane  of,  53*. 

axis  of,  53*. 
Folded  rocks,  53*,  54*,  211,  212*,  213*,  215*. 

effect  of  denudation  upon,  55,  56*. 
Folds,  decapitated,  56*. 
Foliated  rocks,  31. 
Foraminifers,  61*,  62*. 
Fordilla,  247*. 

Forests,  geological  effect  of,  109. 
Formation,  definition  of,  44. 
Fossilization,  99. 
Fossils,  4,  98. 

use  of,  in  determining  age  of  strata,  225. 
Fragmental  rocks,  28,  29,  33. 
Freestone,  35. 

Freezing  water,  action  of,  157. 
Fresh  water,  action  of,  124. 
Fresh-water  limestone,  105. 
Fringing  reefs,  102*. 
Frogs,  85. 


Frondicularia,  61*. 

Fruits,  Carboniferous,  300*,  802. 

Tertiary,  391*. 
Fucoids,  88. 
Fumaroles,  185. 
Fungi,  59,  S7. 

Carboniferous,  802. 
Fusulina,  61*. 

Gabbro,  38. 

Galena  Limestone,  260. 

Galenite,  202. 

Ganges,  detritus  carried  by,  187. 

Gangue,  198. 

Ganoids,  83*,  84*. 

Carboniferous,  306,  307*. 

Cretaceous,  370. 

Devonian,  284,  286*. 

Jurassic,  339,  350,  351*. 

Lower  Silurian,  258. 

Triassic,  339*,  350,  851. 
Garnet,  22*. 

Gas,  natural,  25,  260,  289. 
Gastropods,  73,  74*. 

Cambrian,  247*. 

Carboniferous,  304*. 

Cretaceous,  369,  870,  371*. 

Devonian,  281. 

Jurassic,  346. 

Lower  Silurian,  256*,  257. 

Triassic,  346. 

Upper  Silurian,  269*,  270. 
Gaylenreuth  Cave,  481. 
Geanticline,  55. 
Geanticlines  in  connection  with  mountain- 

makiug,  219. 
Genera,  long-lived,  259. 
Generalized  forms  precede  specialized,  454. 
Genesee  Shale,  277. 
Geode,  47*. 
Geodia,  63*. 
Geographical  progress   in   North  America, 

445. 

Geography,  North  American,  in  Archaean, 
241. 

in  Carboniferous,  313. 

in  Cenozoic,  442. 

in  Champlain  period,  420. 

in  Cretaceous,  363,  364*,  376. 

in  Devonian,  287. 

in  Glacial  period,  419. 

in  Jurassic,  360. 

in  Lower  Silurian,  259. 

in  Mesozoic,  379. 

in  Paleozoic,  317. 

in  Tertiary,  386,  387*,  402. 

in  Triassic,  358. 

in  Upper  Silurian,  272. 
Geological  map  of  England,  295*. 


472 


INDEX. 


Geological  map  of  United  States,  235*. 
Geological  record,  imperfection  of,  461. 
Geological  time,  length  of,  444. 
Geology,  aim  and  subject  of,  1. 

divisions  of,  6. 

dynamical,  6,  9T. 

historical,  6,  223. 

physiographic,  6,  7. 

Btratigraphical,  228. 

structural,  6,  17. 
Georgian  period,  244. 
Geosyncline,  55. 

Geosyncliues  in  connection  with  mountain- 
making,  216. 
Geyser  Canon,  187. 
Geyserite,  36. 
Geysers,  185,  186*. 
Giant's  Causeway,  173, 190. 
Glacial  climate,  cause  of,  169,  418. 
Glacial  period,  405,  406. 

in  Europe,  417. 

subdivisions  of,  415. 
Glacial  scratches,  163,  407*,  408. 
Glaciated  bowlders,  Permian,  299. 
Glacier  theory  of  the  Drift,  409. 
Glacier  torrent,  160. 
Glaciers,  158. 

descent  of,  below  the  snow  line,  159. 

erosion  by,  163. 

method  of  movement  of,  160. 

transportation  by,  162. 
Glauconite,  40,  365. 
Globigerina,  61*. 
Globigerina  ooze,  92, 104. 
Glyptodon,  434*. 
Gneiss,  86,  192,  195. 
Gold-bearing  veins,  199. 
Gondwana-land,  329,  404. 
Goniatites,  281,  282,  283*,  305. 
Gorgonians,  66*. 
Gorner  Glacier,  161*. 
Grammatophora,  88*,  892*. 
Grammostomum,  61*. 
Grammysia,  283*. 
Granite,  20,  86,  195, 198,  199. 
Graphite,  24,  107,  240. 
Graptolites,  255*. 
Gravel,  88. 

Great  Lakes,  Quaternary  history  of,  423. 
Green  Mountains,  Archaean  rocks  in,  238. 

glacial  scratches  on,  408. 
Greenland,  as  illustrating  Glacial  period,  410. 

recent  changes  of  level  in,  428. 
Greensand,  40,  365,  866,  889. 
Grifflthides,  822. 
Grit,  84. 

Cauda-galli,  276. 

Millstone,  296. 

Schoharie,  276. 


Ground  moraine,  163. 
Ground  pines.    See  Lycopods. 
Group,  definition  of,  43. 
Grypha-a,  346,  347*,  369*. 
Guadeloupe,  human  skeleton  of,  440*. 
Guano,  105. 

Gulf  Stream,  93,  151,  168. 
Gymnosperms,  90*. 

Carboniferous,  300*,  302. 

Cretaceous,  367. 

Devonian,  281. 

Jurassic,  336,  337*. 

Triassic,  336,  337*. 
Gypsiferous  formation,  384. 
Gypsum,  117,  267. 
Gyrodus,  84*. 

Hadrosaurus,  372. 
Halicalyptra,  63*. 
Halysites,  269*,  270. 
Hamilton  epoch,  277. 
Hamilton  period,  277. 
Hastings  Sand,  366. 
Hawaii,  map  of,  179*. 

volcanoes  of,  177*,  178,  179*. 
Heat,  167. 

derived  from  chemical   and   mechanical 
action,  171. 

effects  of,  172. 

internal,  evidences  of,  170. 

sources  of,  167. 
Helderberg.    See  Lower  Helderberg,  Upper 

Helderberg. 
Helix,  74*. 

Hematite,  26,  111,  202. 
Henry  Mountains,  190. 
Herculaneum,  184. 
Hesperornis,  374,  375*. 
Heterocercal  tails,  81,  82*,  88*. 
Hexapods,  79. 
Highlands  of  New  Tork  and  New  Jersey, 

238. 

Himalayas,  elevation  of,  403,  404. 
Hipparion,  399*. 
Hippurites,  870*. 
Historical  geology,  6,  223. 
Holoptychius,  286*. 
Holyoke,  Mount,  333. 
Homalonotus,  269*,  322,  328. 
Homocercal  tails,  83,  84*. 
Hood,  Mount,  177. 
Hornblende,  21. 
Hornblende  gneiss,  37. 
Hornblende  granite,  37. 
Hornblende  schist,  38. 
Horn  stone,  107. 
Horse,  genealogy  of,  399*. 
Hot  springs,  185. 
Hualalai,  Mauna,  178. 


INDEX. 


473 


Hudson  epoch,  253. 
Hudson-Champlain  Valley,  821. 
Huron  Shale,  278. 
Hyaena  spelsea,  431. 
Hybodus,  82*. 
Hydra,  64,  65*. 
Hydraulic  limestone,  40. 
Hydromica,  20. 
Hydromica  schist,  87. 
Hydrozoans,  64,  65*. 

Lower  Silurian,  255*. 
Hyena,  cave,  431. 
Hyolithes,  247*. 


Ice,  action  of,  158. 
Icebergs,  151,  165. 
Iceland,  geysers  of,  185. 
Ichthyornis,  374,  377*. 
Ichthyosaurs,  3o2,  353*. 
Idaho  lava  sheet,  189. 
Igneous  eruptions.    See  Eruptions. 
Igneous  rocks,  29,  86,  37,  88,  89,  175, 188. 
Iguanodon, 872. 
Illaenus,  322. 
Illimsni,  177. 

Imperfection  of  geological  record,  461. 
Infusorial  deposits.     See  Diatomaceous  de- 
posits. 

Ink  bags  of  fossil  Cephalopods,  349*. 
Inoceramus,  369*. 
Insectivores,  Tertiary,  394,  400. 
Insects,  79. 

Carboniferous,  305,  306*. 

Devonian,  281,  282,  284*. 

Jurassic,  350*. 

Lower  Silurian,  258. 

Tertiary,  393. 

Triassic,  338,  339*. 
Interglacial  epochs,  416. 
Interior  of  earth,  heat  of,  170. 

solid  or  liquid,  204. 
Intrusive  sheets  of  igneous  rock,  188. 
Invertebrates,  Age  of,  229,  244. 
Irish  deer,  431. 
Iron,  deoxidation  of,  115. 

oxidation  of,  111. 
Iron  Age,  436. 

Iron  carbonate.    See  Siderlte. 
Iron  ores,  26,  202. 

Archaean,  238*. 

Carboniferous,  297. 
Iron  oxides,  26. 
Iron  sulphides,  27. 
Ironstone,  28. 
Iroquois  beach,  423,  424. 
Isastrea,  66*. 
Isostasy,  206. 
Itacolumite,  35. 


James  Elver  stage,  864. 

Jasper,  19. 

Java,  fossil  man  in,  489. 

volcanoes  of,  188. 
Jelly  fishes,  65*. 
Joints,  47*,  219. 
Jura,  Alpine  bowlders  on,  409. 

elevation  of,  404. 
Jurassic  era,  229,  831,  882. 

Kames,  417. 

Kangaroo,  88. 

Kaolin,  34,  114,  116. 

Kea,  Mauna,  177*,  178. 

Kettle  holes,  417. 

Keuper,  334. 

Keweenaw  formation,  245. 

Keweenaw  Point,  copper  veins  of,  201, 

Kilauea,  178. 

Kirkdale  Cavern,  431. 

Kitchen  middens,  488. 

Kjokkenmodingr,  488. 

Krakatoa,  183. 


Labrador  Current,  93. 

Labradorite,  20. 

Labyrinthodonts.    See  Stegocephala. 

Laccoliths,  190. 

Laelaps,  372. 

Lafayette  formation,  417. 

Lahontan,  Lake,  425. 

Lake  Champlain,  etc.    See  Champlain,  etc. 

Lake  dwellings,  439. 

Lakes,  saline,  117. 

Lamellibranchs,  72*. 

Cambrian,  247*. 

Cretaceous,  369*,  370*. 

Devonian,  281,  282,  283*. 

Jurassic,  346,  847*. 

Lower  Silurian,  256*,  257. 

Tertiary,  893. 

Triassic,  346. 

,  Upper  Silurian,  269*,  270. 
Lamination,  31. 
Lamna,  82*,  394*. 
Lampreys,  81. 
Lancelet,  81. 
Landslides,  146. 
Laramide  revolution,  888. 
Laramie  epoch,  365,  866. 
Lava,  30,  38,  39,  175. 
Layer,  42. 
Lead  ores,  202. 
Lemurs,  Tertiary,  394,  400. 
Leperditia,  271*. 

Lepidodendron,  279*,  280,  800*,  801,  810*. 
Lepidosteus,  84*. 
Leptsena,  256*,  269*. 


474 


INDEX. 


Leptocardians,  80. 
Leptomitus,  246*. 
Leptostracaus,  78. 

Cambrian,  249*. 

Level,  changes  of,  in  Quaternary,  419,  420, 
424,  425. 

causes  of  change  of,  203. 
Lias,  335. 
Libellula,  350*. 
Lichas,  822. 
Lichens,  87. 
Life,  agency  of,  In  rock-making,  98. 

Archaean,  240. 

Cambrian,  245. 

Carboniferous,  299. 

change  of,  at  close  of  Mesozoic,  384. 

change  of,  at  close  of  Paleozoic,  329. 

Cretaceous,  867. 

Devonian,  278. 

general  laws  of  progress  of,  232,  450. 

Jurassic,  336. 

Lower  Silurian,  254,  259. 

marine,  distribution  of,  91. 

marine,  earlier  than  terrestrial,  456. 

Mesozoic,  381. 

Paleozoic,  321. 

protective  and  destructive  effects  of,  109. 

Quaternary,  429. 

Tertiary,  390. 

Triassic,  336. 

Upper  Silurian,  268. 
Light,    as  limiting   distribution   of  life  in 

depth,  94. 
Lignite,  25. 
Lily  encrinite,  67*. 
Limestone,  32,  40,  99. 

Bird's-eye,  253. 

Black  River,  253. 

Chazy,  253. 

Corniferous,  276. 

Crinoidal.  294. 

Dudley,  268. 

fresh-water,  105. 

Galena,  260. 

hydraulic,  40. 

lithographic,  335. 

Lower  Helderberg,  267. 

magnesian.  23,  253. 

metamorphic,  41. 

Mountain,  296. 

Niagara,  266,  273. 

Nummulitic,  390. 

Onondaga,  276. 

oolitic,  40,  46,  102,  835. 

Trenton,  253. 

Upper  Helderberg,  276. 

Wenlock,  268. 

Limonite,  27,  111,  113,  116*V297. 
Limulus,  79. 


Lingula,  106,  155*,  247. 

range  of,  in  time,  259. 
Lingula  Flags,  245,  247. 
Lingulella,  247*. 
Links,  missing,  460. 
Lion,  cave,  431. 
Liriodendron,  367*. 
Lithographic  limestone,  835. 
Lithologic  characters,  as  criterion  of  age  of 

rocks,  225. 
Lithostrotion,  304*. 
Lituola,  61*,  368*. 
Liverworts,  88. 
Lizards,  85. 

Cretaceous,  874. 

Jurassic,  356. 
Llandeilo  Flags,  252,  254. 
Llandovery  beds,  268. 
Loa,  Mauna,  177*,  178, 180,  183,  184. 
Lobster,  76,  78. 

Lobworm,  geological  action  of,  110. 
Loganograptus,  255*. 
Loligo,  75*. 
Lophophore,  70*,  71*. 
Lower  Helderberg  period,  265,  267,  278. 
Lower  Silurian  era,  228,  252. 
Lowlands.    See  Plains. 
Ludlow  group,  268. 
Lychnocanium,  63*. 
Lycopods,  89. 

Carboniferous,  300*,  301. 

Devonian,  279*,  280. 

Machaeracanthus,  284*. 
Machaerodus,  431. 
Made,  22. 
Macrurans,  78. 

Magnesian  limestone,  23,  253. 
Magnetite,  27,  202. 
Malacostracans,  77*,  78. 
Malm,  335. 
Mammals,  85. 

Age  of,  231,  386. 

Cretaceous,  374. 

Eocene,  primitive  character  of,  895. 

Jurassic,  345,  357,  358*. 

Quaternary,  430,  432*,  433*,  434*. 

Tertiary,  394,  395*,  397*,  398*,  399*,  400*, 
401*. 

Triassic,  345*,  357. 
Mammoth,  431,  433. 

picture  of,  by  men  of  Reindeer  epoch, 

437,  438*. 

Mammoth  Cave,  143*,  144. 
Mammoth  coal  bed,  298. 
Man,  Ape  of.  232.  405. 

fossil  remains  of,  436. 

modern  relics  of,  440*. 
Mantellia,  337*. 


INDEX. 


475 


Map   of  England   and    southern   Scotland, 

geological,  295*. 
Map  of  Hawaii,  179*. 

Map  of  land  hemisphere  and  water  hemi- 
sphere, 8*. 

Map  of  Mammoth  Cave,  143*. 
Map  of  Maui,  129*. 

Map  of  North  America,  after  Appalachian 
revolution,  328*. 

at. close  of  Archaean,  287*. 

Carboniferous,  287*. 

Cretaceous,  364*. 

Tertiary,  387*. 

Upper  Silurian,  264*. 
Map  of  ocean,  bathymetric,  10*,  11*. 
Map  of  Pennsylvania  coal  areas,  292*. 
Map  of  region  south  of  Long  Island,  bathy- 
metric, 13*. 
Map  of  Tahiti,  130*. 

Map  of  United  States  and  Canada,  geological, 
235*. 

Quaternary,  412*,  413*. 
Marble,  41. 
Marcasite,  27,  112. 
Marcellus  Shale,  277. 
Margarita,  74*. 
Marine  formations,  152. 
Marine  life,  distribution  of,  91. 

earlier  than  terrestrial,  456. 
Marl,  40. 

Marsipobranchs,  81. 
Marsupials,  86. 

Cretaceous,  376. 

Jurassic,  345,  357,  358*. 

Quaternary,  434. 

Tertiary,  398,  400. 

Triassic,  345,  357. 
Massive  rocks,  81. 
Mastodon,  Quaternary,  482*. 

Tertiary,  401. 
Mastodonsaurus,  352*. 
Mauch  Chunk  Shale,  294. 
Maui,  map  of,  129*. 

valleys  in,  129*,  181. 
Manna  Hualalai,  etc.    See  Hualalai,  etc. 
Mechanical  action,  as  source  of  heat,  171. 
Medina  epoch,  266,  273. 
Medus*,  65*. 

Megaceros  Hibernicus.  See  Cervus  euryceros. 
Megalosaurus,  354. 
Megatherium,  433*. 
Meionornis,  441. 
Melosira,  88*,  392*. 
Menevian  group,  230. 
Mentone  skeleton,  488. 
Mer  de  Glace,  159. 
Merostomes,  79. 
Mesolithic  epoch,  487. 
Mesozoic  life,  characteristics  of,  381. 


Mesozoic  time,  228,  229,  330. 

change  of  life  at  close  of,  884. 

disturbances  at  close  of,  388. 
Metamorphic  rocks,  80,  85,  86,  87,  88,  89,  41, 

191,  238. 
Metamorphism,  190. 

agencies  concerned  in,  198. 

dynamic,  195. 

effects  of,  192. 

in  connection  with  mountain-making,  218. 

local,  190. 

regional,  191. 
Miamia,  306*. 
Mica,  20. 
Mica  schist,  36. 
Michigan,  coal  area  of,  293. 
Microdon,  283*. 

Migrations  in  the  Quaternary,  429. 
Millepore,  65. 
Mineral  coal.    See  Coal. 
Mineral  oil.    See  Oil. 
Mineral  waters,  145. 
Minerals,  18. 
Miocene  period,  886. 
Missing  links,  460. 
Mississippi  River,  124,  187. 

delta  of,  139*,  140. 
Moas,  extinction  of,  441. 
Molluscoids,  69,  70*,  71*. 

Cambrian,  247*. 

Carboniferous,  303,  304*. 

Devonian,  281,  282,  283*. 

Jurassic,  346,  347*. 

Lower  Silurian,  256*. 

Triassic,  346. 

Upper  Silurian,  269*,  270,  271*. 
Mollusks,  72*,  74*,  75*. 

Cambrian,  247*. 

Carboniferous,  304*. 

Cretaceous,  369*,  370*,  371*. 

Devonian,  281,282,283*. 

Jurassic.  346,  347*.  349*. 

Lower  Silurian,  256*,  257. 

Tertiary,  393. 

Triassic,  346,  348*. 

Upper  Silurian,  269*,  270,  271*. 
Monkeys,  Tertiary,  395,  402. 
Monocline,  55. 
Monocotyledons,  90*,  91. 
Monotremes,  85. 

Cretaceous,  376. 

Jurassic,  345,  357. 

Triassic,  345*,  357. 
Montana  epoch,  365. 
Monte  Somma,  176*,  188. 
Monticulipora,  257. 
Moraine  profonde,  163. 
Moraines.  162. 

of  Glacial  period,  416. 


476 


INDEX. 


Morcles,  Dent  de,  54*. 
Monnolucoides,  339*. 
Mosasaurs,  878*,  374*. 
Mosses,  88. 

Mount  Etna,  etc.    See  Etna,  etc. 
Mountain  chains,  210. 

height  of,  in  relation  to  size  of  oceans,  16. 
Mountain  Limestone,  296. 
Mountain  ranges,  location  of,  207. 

origin  of,  207. 

process  of  formation  of,  216. 

structure  of,  210. 

unsymmetrical,  914,  216. 
Mountain  systems,  210. 
Mountain-making,  at  close  of  Archaean,  240. 

at  close  of  Jurassic,  862. 

at  close  of  Lower  Silurian,  261,  320. 

at  close  of  Mesozoic,  383. 

at  close  of  Paleozoic,  211,  212*,  213*,  326. 

in  Tertiary,  402. 

slowness  of,  221. 
Mountains,  height  of,  8,  204. 
Mountains  of  circumdenudation,  183. 
Muck,  109. 
Mud,  34. 
Mud  cones,  187. 
Mud-cracks,  156*,  174. 
Muschelkalk,  334. 
Muscovite,  20. 
Myriopods,  79. 

Carboniferous,  805,  806*. 

Devonian,  281,  283. 

Natural  selection,  451. 
Nautilus,  75*,  257. 

range  of,  in  time,  259. 
Navicula,  392*. 
Neanderthal  skull,  437. 
Neocene,  386. 
Neocomian,  231. 
Neolithic  epoch,  438. 
Neopaleozoic  section,  229,  243,  268. 
Neve,  159. 

New  Brunswick,  coal  area  of,  292. 
New  Caledonia,  coral  reefs  of,  103. 
New  Jersey,  buried  forest  in,  429. 
New  Red  Sandstone,  299,  385. 
Niagara  epoch,  266,  273. 
Niagara  Gorge,  41,  42*. 

geological  time  measured  by  excavation 

of,  444. 

Niagara  period,  265,  266. 
Nitric  acid,  geological  action  of,  145. 
Nodosaria,  61*. 
Non-articulates,  60. 
North  America,  geographical  evolution  In, 

208,  445. 
map  of,  after  Appalachian  revolution,  828*. 

at  close  of  Archaean,  237*. 


Carboniferous,  287*. 

Cretaceous,  364*. 

Tertiary,  387*. 

Upper  Silurian,  264*. 
Paleolithic  Man  in,  439. 
profile  of,  15*. 
Notidanus,  82*. 
Notochord,  80. 
Nototherium,  434. 
Nova  Scotia,  coal  area  of,  292. 
Nullipores,  88. 
Nummulites,  61*,  390*. 
Nummulitic  Limestone,  390. 

Obsidian,  38,  175. 

Ocean,  bathymetric  map  of,  10*,  11*. 

chemical  action  of,  236. 

depth  of,  8,  204. 

mechanical  action  of,  146. 
Ocean  and  continent,  boundary  of,  12. 
Ocean  basin,  origin  of,  206. 
Ocean  currents,  150. 
Oceans,  7. 

depth  of,  8. 
Ocher,  111. 
Odontidium,  892*. 
Oil,  mineral,  25,  260,  277,  278,  289. 
Old  Red  Sandstone,  278. 
Olenellus,  249*,  322. 
Oligocarpia,  337*,  338. 
Oligocene,  386. 
Oligoclase,  20. 
Olivine.    See  Chrysolite. 
Oneida  Conglomerate,  266,  273. 
Onondaga  Limestone,  276. 
Onondaga  period,  265,  266. 
Oolite,  40,  46,  102,  335. 
Oolitic  period,  835. 
Ooze  of  ocean  bottom,  92. 
Opal,  19. 
Ophiuroids,  68. 
Opossum,  86. 
Orange  Sand,  417. 
Orbit  of  earth,  eccentricity  of,  169. 
Orbulina,  61*. 
Orchestia,  77*. 
Ordovician  era,  228,  252. 
Oregon,  lava  sheet  of,  189. 
Oreodon,  400,  401*. 
Organic  acids,  geological  effect  of,  118. 
Organic  matter,  reducing  action  of,  115. 
Origin  of  species.    See  Evolution. 
Oriskany  period,  276. 
Ornithopods,  Cretaceous,  372. 

Jurassic,  843*,  344,  354. 
Ornithorhynchus,  86. 
Orogenic  movements.    See  Mountain-ranges, 

Mountain-making. 
Orohippus,  399*,  400. 


INDEX. 


477 


Orthts,  247*,  256*,  269*. 
Orthisina,  247*. 
Orthoceras,  248,  256*,  257,  805. 
Orthoclase,  20. 
Orthoclase  rocks,  86. 
Osmeroides,  372*. 
Ostracoids,  77*,  78. 

Triassic,  338,  889*. 

Upper  Silurian,  271*. 
Ostrea,  72*,  393. 
Otozoum,  340*. 
Ouachita  range,  827. 
Outcrop,  51*. 
Overlap,  57. 
Oxen,  Tertiary,  402. 
Oxygen,  geological  action  of,  111. 
Oysters,  Tertiary,  893. 

Palseaster,  68*. 

Palseoblattina,  258. 

Palaeohatteria,  309*. 

Palseoniscus,  83*,  84*,  307*. 

Palaeotherium,  897. 

Palapteryx,  441. 

Paleolithic  epoch,  436. 

Paleontology   and   embryology,   parallelism 

of,  454. 

Paleozoic  life,  characteristics  of,  323. 
Paleozoic  time,  227,  228,  242. 

change  of  life  at  close  of,  329. 

disturbances  at  close  of,  325. 
Palisades,  189,  832,  333. 
Palms,  Cretaceous,  367. 

Tertiary,  391*. 
Paradoxides,  248*,  322. 
Paris  basin,  Tertiary  animals  of,  396. 
Patellina,  368*. 
Paumotu  Archipelago,  108. 
Peat,  107. 

Pegmatite,  198, 199. 
Pelion,  308*. 
Pemphix,  350*. 
Peneplains,  141. 
Pennsylvania,  map  of  coal  areas  of,  292*. 

oil  region  of,  289. 
Pentacrinus,  68*. 
Pentamerus,  269*,  271*. 
Pentremites,  67*,  304*. 
Periods,  geological,  232. 
Permian  glaciated  bowlders,  299. 
Permian  period,  291,  299. 
Petit  Anse,  salt  deposit  of,  26. 
Petrifaction,  99. 
Petroleum.    See  Oil. 
Phacops,  283*. 

Phaenogams.    See  Phanerogams. 
Phalanger,  86. 
Phanerogams,  89,  90*. 

Carboniferous,  802. 


Cretaceous,  867*. 

Devonian,  281. 

Jurassic,  336,  337*. 

Tertiary,  390,  391*. 

Triassic,  336,  337*. 
Phascolotherium,  358*. 
Phenacodus,  395*,  399. 
Phenocryst,  32. 
Phillipsia,  322. 
Phosphatic  formations,  105. 
Phyllite.    See  Slate. 
Phyllograptus,  255*. 
Physiographic  geology,  6,  7. 
Piedmont  belt,  238. 
Pinnularia,  88*,  392*. 
Pinus,  90*. 

Pithecanthropus  erectus,  489. 
Placental  Mammals,  86. 
Placenticeras,  371*. 
Placoderms,  82. 

Devonian,  283,  284,  285*. 

Lower  Silurian,  258. 

Upper  Silurian,  272. 
Plagioclase  rocks,  38. 
Plains,  13. 
Plant    and    animal,    distinctions    between, 

58. 

Plateaus,  18. 
Platephemera,  284*. 
Platyceras,  247*,  269*. 
Pleistocene,  406. 
Plesiosaurs,  Cretaceous,  372. 

Jurassic,  352,  353*,  854. 

Triassic,  852,  354. 
Pleurosigma,  88*. 
Pleurotomaria,  304*. 
Plinthosella,  63*. 
Pliocene  period,  386. 
Pliosaurus,  354. 
Plumbago.    See  Graphite. 
Plutonic  rocks,  20,  36,  37,  88. 
Pocono  group,  294. 
Podozamites,  837*. 
Polycystines.    See  Radiolarians. 
Polyps.    See  Anthozoans. 
Polythalamia.    See  Foraminifers. 
Pompeii,  184. 
Porcellio,  77*. 
Porphyritic  rocks,  81. 
Porphyry,  82,  38. 
Portage  epoch,  277. 

Portland  (Connecticut)  sandstone,  882. 
Portland  (England)  Dirt  Bed,  885. 
Potomac  formation,  333,  364. 
Potsdam  period,  244. 
Pottsville  Conglomerate,  296. 
Prasopora,  256*. 
Predentata,  Cretaceous,  372*. 
Jurassic,  343*,  344*,  354. 


478 


INDEX. 


Present  flora  and  fauna,  progressive  approxi- 
mation to,  456. 
Proboscideans,  Quaternary,  481,  482*. 

Tertiary,  401*. 
Productus,  303,  804*. 
Protannularia,  254*. 
Protocaris,  249*. 
Protozoans,  60,  61*,  62*,  68*. 

Cretaceous,  368*. 

Tertiary,  389,  890*. 
Pseudopods,  62*. 
Pteranodon,  378. 
Pterichthys,  284,  285*. 
Pteridophytes.    See  Acrogens. 
Pterodactylus,  354,  355*. 
Pterophylluin,  337*. 
Pteropods,  74*. 

Cambrian,  247*. 

Upper  Silurian,  270,  271*. 
Pterosaurs,  Cretaceous,  878. 

Jurassic,  352,  354,  355*,  856*. 

Triassic,  352,  854. 
Pudding-stone,  84. 
Pumice,  175. 
Pupa  vetusta,  304*. 
Purbeck  group,  335. 
Pyrenees,  elevation  of,  408. 
Pyrifusus,  74*,  371*. 
Pyrite,  27. 

oxidation  of,  112,  145. 
Pyroxene,  21. 
Pyrrhotite,  27,  112. 
Pythonomorphs,  873*,  874*. 

Quartz,  18*,  198. 
Quartz  syenite,  87. 
Quartzite,  85. 
Quaternary  era,  232,  405. 
Quercus,  Tertiary,  891*. 

Eacodiscula,  63*. 
Radiates,  60. 
Eadiolarian  ooze,  92. 
Eadiolarians,  62*,  68*. 

deposits  of,  106. 
Eagadinia,  63*. 
Rain,  distribution  of,  128. 

erosion  by,  128. 
Raindrop  impressions,  128*. 
Rappahannock  stage,  364. 
Raritan  stage,  364. 
Rays,  82. 

Recent  period,  405,  425. 
Red  Beds,  299. 

Red  clay  of  ocean  bottom.  92. 
Reefs,  coral,  100,  102*,  104*. 
Regelation,  161. 
Reindeer  epoch,  487. 


Reptiles,  85. 

Age  of,  228,  330. 

Cretaceous,  372*,  878*,  374*. 

Jurassic,  340,  348*,  844*,  852,  858*.  855*. 
856*. 

Permian,  308,  809*. 

Tertiary,  894. 

Triassic,  340*,  341*,  342*,  352. 
Resins,  fossils  preserved  in,  99. 
Revolution,  Appalachian,  825. 

Laramide,  383. 

post-Mesozoic,  388. 

post-Paleozoic,  325. 

Taconic,  260. 
Rhfetic  formation,  334. 
Rhamphorhynchus,  856*. 
Rhaphistoma,  256*. 
Rhinoceros,  Quaternary,  481,  482. 

Tertiary,  400,  401. 
Rhizopods,  61*,  62*,  68*. 

Cretaceous,  868*. 

Tertiary,  389,  390*. 
Rhode  Island,  coal  area  of,  292. 
Rhynchocephala,  85. 

Permian,  308,  309*. 
Rhynchonella,  71*,  271*. 

range  of,  in  time.  259. 
Rhynchotreta,  269*. 
Rhyolite,  88. 

Richmond,  diatomaceous  deposit  of,  391, 892*. 
Rill-marks,  155*. 
Ripple-marks,  154*,  155. 
River  terraces,  138,  422,  426*,  427*. 
River  valleys,  form  of,  131. 

making  of,  129. 
Rivers,  energy  of,  125. 

geological  action  of,  124. 

Paleozoic,  320. 

youth  and  age  of,  140. 
Roches  moutonnees,  163*,  164. 
Rock,  definition  of,  17. 
Rock  salt.    See  Salt. 
Rocks,  Archaean,  236. 

calcareous,  32,  40,  99. 

Cambrian,  244. 

carbonaceous,  107. 

Carboniferous,  291. 

clastic,  28,  29. 

consolidation  of,  117. 

constituents  of,  18. 

Cretaceous,  363. 

crystalline.  28,  29,  35,  41,  175,  188,  191. 

Devonian,  276. 

foliated,  81, 191, 195. 

fragmental,  28,  29,  33. 

hydrous  magnesian,  39. 

igneous,  29,  86,  37,  38,  39,  175,  188. 

Jurassic,  333,  834,  335. 

kinds  of,  28. 


INDEX. 


479 


laminated,  81. 

Lower  Silurian,  252. 

massive,  31. 

metamorphic,  30.  35,  86,  37,  38, 39, 41, 191. 

orthoclase,  36. 

Paleozoic,  thickness  of,  in  North  America, 
211,  316. 

phosphatic,  105. 

plagioclase,  38. 

plutonic,  29,  86,  37,  38. 

porphyritic,  31. 

schistose,  31,  191,  195. 

sedimentary,  29. 
mode  of  formation  of,  165. 

shaly,  31. 

siliceous,  32,  35,  106. 

slaty,  81, 

stratified,  41. 

Tertiary,  388. 

Triassic,  832,  834. 

unstratified,  45. 

Upper  Silurian,  266. 

volcanic,  29,  38,  39,  175. 
Rocky  Mountains,  glaciated  areas  in,  414. 

geanticlinal  elevation  of,  402. 
Rodents,  Tertiary,  394,  400. 
Romingeria,  282*. 
Rotalia,  61*,  62*,  368. 
Rudista,  369,  370*. 

Saccammina,  range  of,  in  time,  259. 

Saint  Helen's,  Mount,  177. 

Saint  Lawrence  River  in  the  Quaternary,  421. 

Saint  Peter's  Sandstone,  253. 

Salamanders,  85. 

Saliferous  group,  885. 

Salina  beds,  266,  273. 

Salina  salt  wells,  267. 

Salisbury  Crags,  190. 

Salix,  Tertiary,  867*. 

Salt,  26,  117. 

Cretaceous,  26. 

Subcarboniferous,  296. 

Triassic,  335. 

Upper  Silurian,  267. 
Salt  lakes,  117. 
Sand, 33. 

Sand  scratches,  119. 
Sand-flea,  77*,  78. 
Sandstone,  35. 

Caradoc,  254. 

Catskill,  277. 

Medina,  266,  278. 

New  Bed,  299,  885. 

Old  Red,  278. 

Oriskany,  276. 

Potsdam,  244. 

Saint  Peter's,  258. 
Sanidin,  88. 


Sapphirina,  77*. 
Sassafras,  Cretaceous,  867*. 
Sauropods,  Cretaceous,  872. 

Jurassic,  342,  343*,  854. 
Sauropus,  808*. 
Scaphites,  370,  371*. 
{  Schist,  31,  192,  195. 
Schistose  structure,  31,  192,  195. 
Schoharie  Grit,  276. 
Scolithus,  248*. 
Scoria,  175. 
Scorpions,  79. 

Carboniferous,  305*. 

interrupted  range  of,  in  time,  459. 

Upper  Silurian,  272. 
Scratches,  glacial,  163,  407*,  408. 

made  by  wind-drifted  sand,  119. 
Sea  anemone,  66*. 
Sea  beaches,  elevated,  421. 
Sea  fans,  66*. 

Sea  urchins.    See  Echinoids. 
Seaweeds.    See  Algae. 
Sedimentary  formations,  marine,  152. 
Sedimentary  material,  origin  of,  151,  165. 
Sedimentary  strata,  formation  oi,  165. 
Selachians,  81,  82*. 

Carboniferous,  806,  307*. 

Cretaceous,  370. 

Devonian,  283,  284*. 

Jurassic,  850. 

Lower  Silurian,  258. 

Tertiary,  393,  894*. 

Triassic,  850. 

Upper  Silurian,  272. 
Semi-bituminous  coal,  298. 
Series,  definition  of,  48. 
Serolis,  77*. 
Serpentine,  21,  89. 
Serpula,  101. 
Sertularia,  65*. 
Shale,  81,  85. 

alum,  85. 

Black,  278. 

Cleveland,  278. 

Erie,  278. 

Genesee,  277. 

Hudson  River,  258. 

Huron,  278. 

Marcellus,  277. 

Mauch  Chunk,  294. 

Utica,  253. 

Sharks.    See  Selachians. 
Shasta,  Mount,  177. 
Shrinkage  cracks,  156*,  173*. 
Siderite,  27,  297. 

alteration  of,  112. 
Sierra  Nevada,  crystalline  rocks  of,  219. 

post-Jurassic  elevation  of,  862. 

Tertiary  elevation  of,  403. 


480 


INDEX. 


Sigillaria,  279*,  280,  800*,  801. 

Silica,  18. 

Silicates,  19. 

Siliceous  rocks,  82,  35,  106. 

Siliceous  sinter,  86. 

Silicon  dioxide.    See  Silica. 

Silurian.  See  Lower  Silurian,  Upper  Silurian. 

Sinter,  36. 

Sipbonia,  369*. 

Skiddaw  Slates,  254. 

Slate,  31,  37. 

Slaty  cleavage,  81,  48*,  219. 

Sloths,  Quaternary,  433*. 

Snails,  73,  74*. 

interrupted  range  of,  in  time,  459. 
Snake  River,  lava  sheets  of,  189. 
Snakes,  85. 

Cretaceous,  374. 
Snow  line,  159. 
Soapstone,  21,  89. 
Sodium  chloride.    See  Salt. 
Soil,  34. 

Solenhofen,  lithographic  limestone  of,  835. 
Solfataras,  185. 
Solids,  flowing  of,  205. 
Solva  group,  230. 
Somma,  Monte,  176*,  183. 
Sorata,  177. 

South  America,  recent  changes  of  level  in, 
428. 

profile  of,  15*. 
Sow-bug,  77*.  78. 
Spathic  iron.    See  Siderite. 
Specialized  forms  of  life,  later  than  gener- 
alized, 454. 

Species,  origin  of.    See  Evolution. 
Sphagnum,  107. 
Sphenopteris,  300*. 
Spicules  of  Sponges,  63*,  64. 
Spiders,  79. 

Carboniferous,  305,  306*. 

interrupted  range  of,  in  time,  459. 
Spinax,  82*. 
Spiny  ant-eater,  86. 
Spirifer,  71*,  271*,  283*  303,  304*. 
Spiriferidse,  last  of,  346,  347*. 
Spiriferina,  347*. 
Spirocyathus,  246*. 
Sponges,  63*. 

Cambrian,  246*. 

Cretaceous,  368, 369*. 
Spongiolithis,  392*. 
Spores  of  Lycopods  in  coal,  810*. 
Springs,  hot,  185. 
Squids,  75*,  76. 
Stage,  definition  of,  43. 
Stalactite,  40,  144. 
Stalagmite,  40,  144. 
Starfishes.    See  Asterioids. 


Statuary  marble,  41. 
Staurolite,  23. 
Steatite,  21,  39. 
Stegocephala,  85. 

Carboniferous,  807,  308*. 

Jurassic,  381. 

Triassic,  339,  340*,  351,  352*. 
Stegosaurs,  Cretaceous,  372. 

Jurassic,  344*,  354. 
Stelletta,  63*. 
Stenotheca,  247*. 
Stephanoceras,  347*. 
Stictopora,  256*. 
Stigmaria,  300*,  301. 
Stone  Age,  436. 
Strata,  age  of,  how  determined,  223. 

conformable  and  unconformable,  56,  57*. 

dislocations  of,  50. 

folded,  211,  212*,  213*,  215*. 

maximum  thickness  of,  50. 

original  position  of,  48,  50*. 
Straticulate  structure,  48. 
Stratification,  origin  of,  44. 
Stratified  rocks,  41. 
Stratigraphical  geology,  223. 
Stratum,  definition  of,  41. 
Streptelasma,  256*. 
Strife.    See  Scratches. 
Strike,  51*,  52. 
Strophomena,  269*. 
Strophomenidse,  last  of,  346. 
Structural  geology,  6,  17. 
Subcarboniferous  period,  291,  294. 
Submarine  eruptions,  184. 
Subsidence,  coral  island,  104*,  404. 

effect  of,  on  temperature,  168. 
Subsidence  of  Atlantic  coast  of  United  States, 

429. 

Subsidence  of  Greenland,  428. 
Subsidence  of  volcanic  regions,  184. 
Subterranean  waters,  142. 
Sulphur,  volcanic  deposits  of,  185. 
Sun,  heat  received  from,  167. 
Superimposed  drainage,  142. 
Superior,  Lake,  copper  deposits  of,  201. 
Superposition,    criterion    of   age  of   strata, 

224. 

Sweden,  changes  of  level  in,  428. 
Switzerland,  lake  dwellings  of,  489. 
Syenite,  37. 
Syenite,  gneiss,  87. 
Synclinal  axis,  53*,  55. 
Syncline,  53*,  55. 
Synclinorium,  218. 
Syncoryne,  65*. 
Synthetic  types,  455. 
Syracuse,  salt  wells  of,  267. 
Syringopora,  282*. 
System,  definition  of,  43. 


INDEX. 


481 


Table  lands.    See  Plateaus. 

Table  mountains,  189. 

Tachylite,  39,  175. 

Taconic  mountain  system,  262. 

Taconic  range,  Cambrian  rocks  of,  245. 

elevation  of,  201,  320. 
Taconic  revolution,  260. 
Tahiti,  erosion  in,  130*,  181. 

map  of,  130*. 
Talc,  21. 
Talc  schist,  39. 
Taxocrinus.  256*. 
Teleosts,  83,  84*. 

Cretaceous,  370,  372*. 
'  Jurassic,  351. 

Tertiary,  393. 

Triassic,  351. 
Tellina,  72*. 
Temperature,    as    limiting    distribution 

marine  life,  93. 

Tennessee,  East,  valley  of,  218. 
Tennessee  Island,  263,  288. 
Tentaculites,  270,  271*. 
Terebratula,  71*. 
Terebratulina,  71*. 
Terraces,  river,  138,  422,  426*,  427*. 
Terranes,  17,  41. 

Terrestrial  life,  later  than  marine,  456. 
Tertiary  era,  231,  386. 
Tetrabranchs,  75*. 

Cambrian,  247. 

Carboniferous,  304. 

Cretaceous,  370,  371* 

Devonian,  282,  283*. 

Jurassic,  347*. 

Lower  Silurian,  256*,  257. 

Triassic,  347,  348*. 
Tetractinellid  spicules,  63*. 
Tetradecapods,  77*,  78. 

Jurassic,  350*. 
Textularia,  61*. 
Thallophytes,  8T,  88*. 
Theromorphs,  ;308. 
Theropods,  Cretaceous,  872. 

Jurass'c,  344,  354. 

Triassic,  340*,  341*,  342*,  354. 
Tiaropsis,  65*. 
Tidal  currents,  149. 
Till,  406. 

Time,  geological,  length  of,  444. 
Time  ratios,  317,  379,  444. 
Tisiphonia,  63*. 
Titanotherium,  397*,  400*. 
Toads,  85. 
Tourmaline,  22*. 
Trachyte,  38,  175. 
Trachytic  domes,  184. 
Tracks  of  animals,  250,  286,  307,  308*,  3 
339*,  340*,  341*  352*. 


of 


Transportation,  by  glaciers,  162. 

by  rivers,  136. 

Transporting  power  of  water,  137. 
Trap,  39. 

Travertine,  40,  116,  187. 
Tree  ferns,  89. 

Carboniferous,  301. 
Tremadoc  Slates,  230. 
Trenton  epoch,  253. 
Trenton  period,  252,  253. 
Tresca,  experiments  of,  on  flowing  of  solids, 

205. 

Triarthrus,  258*. 
Triassic  era,  229,  331,  332. 
Triceratium,  392*. 
Triceratops,  372*. 
Trigonia,  346,  347*. 
Trigonocarpus,  300*. 
Trilobites,  77*,  78. 

Cambrian,  248*,  249*. 

Carboniferous,  305. 

Devonian,  281,  282,  283*. 

Lower  Silurian,  256*,  257,  258*. 

range  of  genera  of,  in  time,  322. 

Upper  Silurian,  269*,  270. 
Triloculina,  61*. 
Tripoli,  392. 
Tufa,  35,  175. 

calcareous.    See  Travertine. 
Tuuicates,  79. 
Turrilites,  370,  371*. 
Turtles,  85. 

Cretaceous,  374. 

Jurassic,  356. 

Tertiary,  394. 

Triassic,  356. 

Unconformable  strata,  56,  57*. 

Underclay,  297. 

Ungulates,    Tertiary,  394,  395*,  896,  897*, 

398*,  399*,  400*,  401*. 
United  States,  geological  map  of,  235*. 
Unstratified  rocks,  45. 
Upper  Helderberg  Limestone,  276. 
Upper  Silurian  era,  229,  243,  263. 
Ursus  speltcus,  431. 
Utica  epoch,  253. 

V,  Archaean,  237,  446. 

Valleys,  formation  of,  129,  148. 

Vegetable  kingdom,  86. 

Vegetable  material,  decomposition  of,  810. 

Veins,  196, 197*. 

false,  203. 

material  of,  198. 

origin  of,  198. 

superficial,  201. 
Ventriculites,  63*. 


482 


INDEX. 


Vermes,  7fl. 

Cambrian,  248*. 
Vertebrates,  80,  82*,  83*,  84*. 

Carboniferous,  806,  807*,  808*,  809*. 

Cretaceous,  870,  872*,  878*,  874*,  875*, 
377*. 

Devonian,  283,  284*,  285*,  286*. 

Jurassic,  339,  340,   842,  343*,  344*,  350, 
851*,  353*,  355*,  356*,  357*,  858*. 

Lower  Silurian,  258. 

Quaternary,  430,  432*,  483*,  434*. 

Tertiary,  393,  394*,  395*,  897*,  898*,  899*, 
400*,  401*. 

Triassic,  339*,  340*,  841*,  842*,  845*,  850, 
852*,  357. 

Upper  Silurian,  272. 
Vesuvius,  176*,  177,  182,  186. 
Volcanic  eruptions,  177. 
Volcanic  rocks,  29,  88,  39,  175. 
Volcanoes,  174. 

distribution  of,  171. 

Waldheimia,  71*. 
Warren,  Lake,  424. 

Washington,  Mount,  bowlders  on,  410. 
Water,  action  of,  when  freezing  and  frozen, 
157. 

chemical  action  of,  111,  187, 198, 198,  236. 

mechanical  action  of,  124. 


subterranean,  142. 

transporting  power  of,  187. 
Water-lime  group,  267. 
Waves,  action  of,  147. 
Weald  Clay,  866. 
Wealden  formation,  866. 
Wenlock  Limestone,  268. 
West  Rock,  333. 
Whales,  Tertiary,  394,  398. 
White  Mountains,  glacial  scratches  on,  408. 
Wind,  geological  action  of,  118. 

transportation  of  moisture  by,  128. 
Wind-drift  structure,  121*. 
Wombat,  86. 
Woodocrinus,  804*. 
Worms.    See  Vermes. 

Xiphacantha,  62*. 
Xiphodon,  398. 
Xylobius,  306*. 

Yellowstone  Park,  117,  185, 187, 189. 
Yellowstone  River,  115. 

Zamia,  836*. 
Zaphrentis,  269*. 
Zeuglodon,  398. 
Zoantharians,  60*. 


Lessons  in  Physical  Geography 

By  CHARLES  R.  DRYER,  M.A.,  F.G.S.A. 
Professor  of  Geography  in  the  Indiana  State  Normal  School 


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